12V Battery FAQ

[Mach-Lee]

If adding an aftermarket amp and sub (professionally installed), what should I confirm in terms of proper installation of a power cable to the battery?

The amp wire should be connected to the positive terminal with an eye terminal. There should be a fuse in the wire within 12" of the battery. The wire should be routed through the firewall and under the carpet where it won't be rubbing against anything, not haphazardly through the door opening or under the car. The body ground should be made near the amplifier location.

I have a long cruise planned for April 2024, I will be traveling for 4 weeks. My 2022 Mach E Ex AWD will be at home in a warm garage (SW Florida), nothing I can do. That means I should expect a dead 12V battery upon return, right?

Is there any way to prepare or avoid this altogether, besides staying home? LOL
Maybe leave the frunk proactively open?

No, it shouldn't go dead. You can leave the frunk open if you want, but I think it will be okay. It should recharge automatically if it gets low (this is okay occasionally). Park with the HVB at about 50%.

Good stuff! Thanks for this massive effort to explain a complicated (and controversial) topic.

Question from someone who doesn't drive the car a lot, every day, and often for short trips. It appears the simplest solution to keeping up the 12v charge level is to put the car on a Level 1 charger occasionally (at least for those of us who got one with the car). This seems easier than running the car in the garage for several hours, and certainly less trouble than charging it directly.

True?

Yes.

Can the GTPE replacement battery at Battery plus X2 power premium agm 740cca work?

No, those specs do not match OEM. The replacement battery needs to have very similar specs to the original to work properly.

Sponsored

 

[dimes4slim]

This will cover everything you ever wanted to know about the 12V battery in the Mach-E (also applies to F-150 Lightning).

Click the hidden answers to display them. This is a work in progress, more FAQs may be periodically added or updated. This information comes from my knowledge, experience, and the factory service manual.

What type of 12V battery does the Mach-E have?

The 12V battery is a lead-acid AGM (Absorbed Glass Mat) type. This is very similar to traditional flooded lead-acid batteries which have been used for decades in cars. The difference is how the sulfuric acid electrolyte is stored, rather than the cells being flooded with free liquid, the acid is absorbed into glass matts stuck between the lead plates. As a result, the battery is considered “spill free”, if you shake one you won’t hear any liquid sloshing. AGMs are used in most new cars now because they charge faster and more efficiently than flooded batteries.

Where is the 12V battery?

The 12V battery is located under the hood on the left side of the vehicle (underneath the covers). Look for the embossed ⊕ and ⊖ symbols on the plastic covers, the jump start points are directly underneath these. The center and left side plastic covers must be removed for access (there are multiple clips holding them down, pull up firmly near each clip until you get them all).

Why does the Mach-E even need a 12V battery?

All EV’s need some type of auxiliary battery to run their low voltage systems and switch the high voltage on and off for safety. You cannot have 400V running through a window switch because that would be dangerous. So these components need to run off low voltage DC, 12V is by far the most common standard. The 12V system is also used to run the modules that control the high voltage system, and is used to close the contactors that “switch” the high voltage battery on and off.

What are the 12V battery specifications?

Part number: BHAGM-H3
35 Amp-hours, 380 CCA, 60 RC, 27 lbs
H3 size (175mm x 175mm x 190mm) L x W x H

Is the Mach-E 12V battery smaller than normal? Is this causing 12V issues?

Yes, the H3 size is much smaller than a regular car battery, about half the size. It doesn’t need to be as big because it doesn’t have to crank an engine. No, the smaller size isn't causing the 12V issues. The battery is similar in size to other EVs and is appropriate for the application. The 12V issues are caused by how the battery is managed, not because of it being small.

Can I replace the stock AGM battery with bigger size?

Yes, however this is not recommended because of the additional issues it can cause. The stock battery is an H3 size, the battery tray has another set of holes to hold a larger H4 size battery, which will fit. However, a battery with a larger capacity will not play well with the BMS system. It expects a 35 Ah capacity AGM. The H4 battery is 33% larger, so the BMS will not be able accurately measure or utilize the extra capacity beyond 35 Ah. As a result, the larger battery may be chronically undercharged, causing early failure. In other words, it might make things worse, not better.

Can I replace the AGM battery with a lithium or LFP battery?

No, bad idea. 12V lithium batteries operate at a different voltage setpoint than 12V AGM batteries. The charging and BMS system of the Mach-E is calibrated for AGM chemistry only. If you put in a lithium battery, the BMS will not measure the state of charge % correctly, and the lithium battery may not be charged fully due to the lower voltage setpoint of AGM. For example, while driving the voltage is normally held around 12.9V, this will perfectly maintain an AGM at 100%, but a lithium battery will only be held at 20% SoC. This means a lithium battery will gradually discharge while driving to 20%. Load shed will activate, causing your radio, HVAC, and accessories to shut down while driving.

What precautions do I need to take with AGM batteries?

The worst thing you can do to an AGM is overcharge it. When a lead acid battery is overcharged, water is split into hydrogen and oxygen gas, which is vented out of the battery and permanently lost. Traditional flooded lead acid batteries have plenty of extra electrolyte, so if some boils off it’s not a big deal. But an AGM battery is “starved” of extra electrolyte, so they can not tolerate much electrolyte loss without permanent degradation. An AGM is sealed, so there is no way to add back water. Therefore charging of an AGM needs to be closely regulated, especially at higher voltages. A battery charger designed for flooded lead acid may hold the voltage too high for too long and cause electrolyte loss. This is why it’s important to use a battery charger with an AGM mode.

Other than overcharging, avoid deep prolonged discharge below 50%, as this can cause sulfation. Keep AGMs charged above 80% while not being used. Last, be careful when jump starting an AGM, they can explode just like flooded batteries due to hydrogen buildup and a spark.

Is the voltage of an AGM different than a flooded lead-acid battery?

Yes, the voltage of an AGM is slightly higher than a flooded battery. A fully charged AGM produces 12.85V vs. 12.65V for a flooded battery. The +0.2V difference is significant if you are using a voltage threshold to determine SoC. If you use the voltage thresholds for a flooded battery by mistake, you will be off by about -10% SoC on the AGM.

The charging and float voltage setpoints are also different, which is why you should use a charger with an AGM mode.

What voltage is fully charged?

12.85V (depends slightly on temperature)

What is the BMS?

BMS stands for Battery Management System. It is used to precisely manage the energy level in the 12V battery for maximum efficiency and battery longevity. It consists of a sensor on the negative battery terminal that measures both battery voltage and amperage with a high degree of precision. It uses this data to determine the percent state of charge and capacity of the battery at all times (even while off). Ford started using this system on almost all of their vehicles around 2013. Even though it’s been around for over a decade, the BMS is still poorly understood by many but is vitally important to the function of the entire 12V electrical system.

The primary way the BMS determines the % SoC is by measuring the current flow in and out of the battery over time. It keeps track of how many amps have be drained or charged and can calculate the SoC based off that (amps x hours = amp hours). The SoC is used to control the charging system voltage and to drop accessory loads if the battery gets too low (load shed). The SoC is also important for OTAs, as they require the car to run off 12V battery during installation.

The secondary way the BMS determines the SoC is by measuring the open-circuit battery voltage while the car is off. The voltage reading is used to adjust the SoC to account for minor errors. However this is a very slow process that requires approximately 8+ hours of parked off time to read the battery voltage accurately. The vehicle must he UNDISTURBED during this period or the BMS will not be able to accurately determine the SoC. Vehicles that are woken up or driven frequently with no breaks may have difficulty with this process.

What is BMS data quality?

BMS data quality refers to the confidence of the battery SoC reading based on the standby open circuit voltage. The BMS requires an ~8-hour rest period with a constant sensed voltage to read SoC with high confidence. If the rest period is disturbed in some way and the BMS does not have a recent reading of sufficient accuracy, the data quality will be flagged as poor. Disruptions include opening doors, walking near the car with a fob or PAAK, driving the vehicle, remote data pings, connecting a battery charger with a fluctuating voltage, resetting the BMS. Additionally, if there is an excessive standby drain of greater than 200 mA (e.g. dashcams), the BMS cannot accurately read the SoC.

Importantly, if BMS data quality is poor, an OTA will not install since sufficient battery capacity is not assured. Remove standby drains, chargers, and park the vehicle away from fobs (such as on the street) undisturbed for 8+ hours to fix.

What is SoC?

SoC stands for State of Charge. It’s how full your battery is in percent.

Where can I see the 12V SoC percentage?

Unfortunately, the 12V SoC % is not easily accessible to the user. It is not shown anywhere on the screens or in FordPass. It requires an OBD-II scan tool to read. For a limited time, you can view your 12V charge level on Ford's website here.

Can I determine the SoC based on the voltage?

Not easily. Battery voltage will fluctuate based on the current draw on the battery, and whether it’s being charged. The battery could be at 70% SoC and have a voltage anywhere from 11.5V to 15.2V. This is why the car uses SoC instead of voltage to determine the 12V state. The only time SoC can be inferred from voltage is when the battery has been sitting undisturbed for at least an hour (open circuit or resting voltage) which must be measured under specific conditions (see below).

I measured the voltage with the car off and it was only 12.0V, is the battery low?

Not necessarily. First of all, you need to measure the voltage the correct way with no loads. This means letting the car go to sleep for 30 minutes before a measurement. If you just open the hood and immediately make a measurement, it will be wrong because you just woke the car up by opening the hood. You must open the hood, wait 30+ minutes, and then make a measurement without disturbing the car. Also, if your phone or fob is in your pocket and you walk up to the car, you just woke it up (so keep your phone and fob well away when taking a voltage reading). In most cases, the voltage will come back up after you let the car go to sleep. If the resting voltage after 30 mins truly is 12.0V or less, then the battery is low and should be recharged.

What % SoC should the 12V battery have normally?

Typically above 70% on regularly driven vehicles. If your vehicle has been sitting for a few days, the 12V may be down to 50%.

An AGM should be kept above 50% SoC (12.0V) to prevent damaging sulfation. If you notice the resting voltage is below 12.0V or 50%, the AGM should be recharged as soon as possible. When driving, the 12V battery will charge to about 90%, possibly higher. When the car is parked, the SoC will slowly decline with time.

What % SoC does an OTA need to install?

It varies. Some OTAs require a higher percentage than others. It also depends on your current battery capacity and age. The exact threshold is calculated by the vehicle right before an OTA installs. The system ensures an adequate number of amps hours will be left in the battery after the OTA is finished to prevent bricking. If the reserve capacity calculation comes up short, the OTA will not install.

Longer OTAs such as 6.6.0 will typically require about 80% minimum. Shorter OTAs may only require 50%. This is why some OTAs are harder to install than others. Again, the exact threshold will vary from vehicle-to-vehicle based on battery capacity differences. If your 12V is failing and has poor capacity (as determined by the BMS), you may not be able to install OTAs even when charged to 100%. 12V battery replacement is necessary at this point.

How long does it take to charge the 12V battery to 100%?

This varies considerably depending on battery temperature, condition, aging, and charger output. A new battery at room temperature may only take 3 hours. In the winter, a cold sulfated battery may take as long as 24 hours to reach 100%. The last portion of the charging from 90% to 100% takes significantly longer. The charging rate is not linear, it's an exponential decay in rate.

How much 12V battery drain is normal while parked?

Ideally, less than 5% loss per day. There are two types of drain, standby (or quiescent) drain, and periodic drain. Standby drain is a constant 24/7 low-level load when the car is fully asleep. This includes listening for nearby key fobs or PAAK, or incoming cellular pings from Ford. The quiescent current can be read from the BMS with a scan tool, and should normally be less than 50 milliamps. If there is a problem with a module not going to sleep, or an aftermarket dashcam is improperly installed to constant-on power, the standby drain will exceed 50 mA and can cause the battery to drain too quickly. Excessive quiescent current will also prevent the BMS from reading the SoC correctly.

The other type of drain is periodic, this happens whenever the car is woken up. There are many things that can wake up the car, including opening a door, walking near the car with a key fob or PAAK present, forcing a FordPass data refresh, 3rd party apps pinging the car, periodic data upload/download session, etc. You may hear a clunking noise from the car when it’s woken up. Battery drain can peak above 10A for a short time until gradually decreasing as modules go back to sleep. It takes about 10-15 minutes for the car to go fully back to sleep after each wakeup, and will sap about 2-3% from the battery each time. In some cases, the car is woken up dozens of times per day, which can drain the 12V significantly faster than 5% per day.

What type of 12V battery charger should I get?

The battery charger should be 4 amps or larger and have an AGM mode. This will ensure the battery will charge in a reasonable timeframe at the correct voltage. The charger should also be temperature compensated, meaning it adjusts the charging voltage based on the ambient temperature. Charging voltage needs to increase in cold conditions and decrease in warm conditions to properly charge the battery. Do not use a trickle charger to charge a battery, they take too long to be effective.

If the battery is completely dead, you will need to perform a jump start first (with a jump pack or jumper cables) before you can charge the battery, because the Mach-E will draw more amps than the charger can provide while trying to cold boot.

Should I install a battery maintainer?

Most people do not need to use a battery maintainer. Managing your driving and charging strategies is a better approach (see other FAQs). I only recommend a maintainer if you are going to regularly park the vehicle for more than a week at a time. If you are going on a vacation two weeks or less, you can just park the vehicle (recommend parking with the HVB around 50%).

Where do I connect a 12V battery charger?

Connect the charger to the jump start points under the hood, left side. See photo. You’ll need to remove the frunk covers first, see the battery location FAQ. IMPORTANT: DO NOT CONNECT THE BATTERY CHARGER TO THE NEGATIVE BATTERY TERMINAL. You must use a body ground, such as the negative jump post on the left side strut tower. See below FAQ for more information on why this is critical.

FYI the emergency leads in the front bumper are not connected to the 12V battery, thus you cannot charge the battery with them. They are for opening the frunk only.

Is there a wrong way to connect the battery charger?

YES! YOU MUST USE A BODY GROUND! DO NOT CONNECT ANYTHING TO THE NEGATIVE BATTERY TERMINAL! A body ground is anywhere on the body besides the negative battery terminal. You can use the negative jump post on the strut tower. Why is this critical? If you connect a charger or power supply to the negative battery terminal, you will bypass the battery current sensor, and the BMS will think the battery is discharging (SoC % will go down) instead of charging since the current is flowing through the sensor in the wrong direction. The BMS thinks the battery is going dead (even though it’s charging) and will activate load shed modes by shutting down modules and features, causing extremely odd vehicle behavior. You will think your car is possessed.

I cannot stress how important it is to connect the charger to body ground properly because it will wreak havoc with the vehicle’s systems if you do it wrong.

What does “System Off to Save Battery” on the touchscreen mean?

This means the BMS thinks the 12V battery is getting low (below 50%) and is switching off accessory loads to save battery power (this is called load shed mode). If you see this message, immediately turn the car fully ON (if not already on) so the 12V battery can charge. The message should go away in a few minutes. If the message does not go away, or pops up while driving, this could indicate a serious issue with your 12V battery or charging system and warrants an immediate dealer trip.

Does plugging in the car keep the 12V battery charged?

NO! That is one of the biggest misunderstandings of the Mach-E 12V system that I see. The 12V battery is only charged when the vehicle is ON or CHARGING. If the vehicle is plugged in and NOT charging, the 12V battery is NOT charged. So if the vehicle was not driven or charged very long or very recently, the 12V battery is not going to be full. Some people think plugging in works like a 12V trickle charger, that is NOT the case.

But won’t the 12V automatically recharge when low?

Yes, but this is designated to be a failsafe against the battery going completely dead rather than a regular occurrence. This recharge event does not occur until the SoC is all the way down to 30-40% (quite low). This is well past the point of significant sulfation formation, and past the point the battery will freeze in cold temps. Repeated deep recharge events are stressful cycling on the battery and should be avoided. Automatic recharge is also disabled when the HVB is below 20%—the 12V battery will be allowed to go completely dead. Which is another reason it shouldn't be relied upon. For example, people with improperly wired dashcams have parked their car with <20% and the dascham completely drains the 12V battery, resulting in a lock out.


What should I do if I don’t drive a lot? Or take short trips?

This can be a difficult situation for the 12V battery because it doesn’t have enough time to fully recharge with short or infrequent trips. As a result, the battery can become chronically sulfated which causes the capacity to decrease. One thing you can do to help is structure your charging so it occurs in long continuous sessions. For example, drive the car below 50% before recharging to 90%, which will result in a long charging session. Another suggestion is to use a 120V L1 EVSE instead of L2 if you don’t drive much, this means longer charging times which is good for the 12V battery. Or if you have a smart EVSE, reduce the amp setting as low as you can.

Another approach is to just leave the car on in the garage once a week. Disable auto shutdown timer, shut off HVAC, and leave the car on for about 2 hours.

Last approach is to use a maintenance or trickle charger, although this more work and requires 12V battery access.

Will running the car in park charge the 12V battery?

Yes, you can leave the car on for a while to charge the 12V battery. How long varies, at least 30 minutes, but If the battery is very low you'll need more like 3+ hours to charge it. Disable auto shutdown timer in settings if you want it to run longer than 30 minutes.

What happens when the 12V battery goes dead? How do I get in the car?

If the 12V battery goes completely dead, you’ll need a jump start to get into the car if it’s locked. Because there is no key cylinder anymore, there is a special access procedure to open the frunk and jump start the 12V battery. You will need a 12V jump pack or jumper cables to open the frunk (NOT a battery charger! Battery chargers won’t work!). The procedure is covered in the owner’s manual and numerous videos, search for details. In a nutshell, you will need to pull out the emergency leads through the access panel in the front bumper, apply 12V to them to open the frunk, then remove the frunk panels and jump start the 12V battery using the provided jump terminals. NOTE: The bumper leads are not connected to the 12V battery. Their only purpose is to power the motor that opens the frunk, that’s it. You must apply power from a jump pack or jumper cables to fully power up the vehicle. The Mach-E has a huge inrush current demand on startup, so you need a powerful jump pack (rated for V8 or diesel engines) or traditional jumper cables. I recommend lithium jump packs rather than the traditional/older lead acid type.

If your Mach-E died while unlocked, the doors should still open after pressing the button TWICE. Then you can open the hood from inside and jump the 12V as described above.

Again, a battery charger will not work due to the inrush current demands required.

Can I jump start other disabled vehicles with the Mach-E?

Ford does not recommend this. The 12V battery in the Mach-E is small and there are risks to the electrical system electronics and headlights if there is a large voltage dip or surge while jump starting another vehicle. Do not jump start another vehicle unless it is a true emergency.

How often does the 12V battery need to get replaced?

Every 2-6 years depending on your climate and usage level. Heat kills batteries, so the hotter the climate, the shorter it will last. If you live in the southern US, 2-4 years is typical. If you live in the northern US or Canada, 4-6 years is typical. It also depends on usage. FYI if you have a dashcam that drains the 12V battery, your battery will wear out approximately 2x faster than normal (it might only last a year or two with a dashcam).

Is my 12V battery going bad?

If you get warnings in FordPass about your 12V battery, the vehicle frequently enters deep-sleep mode in FordPass, you have a lot of difficulty getting OTAs to install, or notice other odd symptoms, it is possible the 12V battery is going bad. Have the battery tested with a digital battery analyzer by your dealer or other professional and replace as necessary. Also consider reconditioning the 12V battery per my topic to restore some lost capacity.

What are some signs my 12V battery is extremely low?

Common warning signs are the startup chimes sounding antiquated (because they are played through the instrument cluster instead of the speakers), a repetitive thumping or popping noise coming from the speakers, false door-opened intrusion alarms (if you’re sure the doors weren’t opened), and a message on the instrument cluster that says “System off to save battery”.

Will my dashcam cause problems with the 12V battery?

Yes, if you wire it improperly. It is very important that the dashcam does not drain the 12V battery when the vehicle is off. It is strongly recommended that the dashcam is wired to switched accessory power only, which is depowered about 15 minutes after the car is shut off to save the 12V battery. The Mach-E 12V battery is small, only about half the size of a regular car battery, so it drains twice as fast. Dashcams can cause problems with low 12V state of charge and chronic sulfation, which may cause additional problems such as OTAs not installing, the center screen to stop working “System off to save battery”, odd vehicle glitches such as thumping speakers, or a completely dead battery and unresponsive vehicle. Excessive key-off load from a dash cam can also interfere with the BMS’s ability to read the 12V percentage accurately, and you may receive 12V drain notifications in FordPass. Last, running an improperly wired dashcam will cause your 12V battery to wear out much faster than normal due to excessive cycling, in as little as a year.

In comparison, a dashcam wired to run only when the vehicle is ON will cause none of these problems.

Can I install an always-on dashcam with a parking mode enabled?

Yes, but this strongly not recommended on the Mach-E due to the 12V issues it can cause (see above FAQ). A lot of people want Sentry Mode, but the Mach-E 12V system was not designed for this. Sentry Mode on a Tesla keeps the 12V system on 24/7 so the 12V battery doesn’t drain. This is not possible on the Mach-E, so installing an always-on dashcam WILL drain and degrade the 12V battery.

If you absolutely must run a dashcam in parking mode, it should be tightly controlled to shut off before the 12V battery is excessively drained. The cutoff voltage must be set to 12.2V or higher (60%). The default of 12.0V (40%) a lot of cameras use is too low! Understand that by doing this, you will need to replace your 12V battery more often, perhaps every two years due to extra wear and cycling.

A better alternative is to install a dashcam battery pack, which is a separate battery the dashcam runs off while the car is off. When the vehicle is turned on, the dashcam battery will automatically recharge. There is no key-off drain on the Mach-E battery this way.

Can installing a dashcam or other 12V accessory void the warranty on my 12V battery?

Yes. If wired improperly to cause a constant drain, Ford is not responsible for the excessive wear and tear on the 12V battery that an always-on dashcam will cause. If the dealer finds the dashcam or accessory is the cause of a 12V drain or worn-out battery, you may have to pay for the service visit or replacement 12V battery yourself. 12V accessories shall only be wired to switched accessory power per Ford. (Using the provided 12V power and USB ports is totally fine since they are switched.)

How is the 12V battery charged?

Instead of an alternator being turned by an engine, the Mach-E uses something called a DC-to-DC Converter. This is a box that converts high voltage 350V DC from the big battery to low voltage 12V DC for the small battery. This DC/DC inverter is only active and charging when 1) the car is turned on and 2) while charging the high voltage battery. When the car finishes charging, the DC/DC is turned off and the 12V battery is no longer charged. The DC/DC can also be switched on in special situations such as if the 12V battery is about to go dead, or if an OTA is installing (only certain OTAs).

What is the base load on the electrical system?

The base load is about 20 amps (260W) with the car on and all accessories off.

How many amps can the DC/DC converter output?

The standard Mach-E DC/DC can output 160 amps peak. GT models have a larger unit that can output 220 amps peak. The typical load on the 12V system is anywhere from 20-150 amps depending on accessories used (headlights, blower motor, rear defrost, power steering rack, radiator fan, etc). Continuous loads shall be less than peak output. NOTE: The base vehicle (non-GT variant) does not have capacity for additional loads beyond vehicle standard equipment. This vehicle configuration should not be used for applications that add aftermarket equipment.

How big of an 120VAC inverter can I wire to the 12V system?

Do this at your own risk, see above. To prevent overloading the electrical system, use a 1500W inverter or less (<2000W for GT only). A 1500W inverter running at 80% efficiency will draw about 150 amps full load. Do not run more than 80% continuous load (1200W) because the DC/DC converter output wire will get very hot and may overheat. During use, the car must be switched fully ON (disable power-down timer if necessary) and all accessories must be turned off. Monitor the high voltage battery and discontinue use at 20%.

Will using the accessory mode (green light blinking) cause the 12V battery to drain?

YES! The 12V battery is not continuously charged in accessory mode and will drain just like in an ICE vehicle. If you want to listen to the radio while parked, always turn the car FULLY ON (solid green light on Start/Stop button). I recommend not using accessory mode ever, there’s no point. It’s a legacy ICE holdover that should have been eliminated.

Why are there so many problems with the 12V battery?

This is complicated to answer since there are several factors that contribute to 12V issues. But in my opinion, the largest factor is that the charging logic does not sufficiently maintain the 12V battery at high states of charge when the vehicle is parked. The car also wakes up from sleep an excessive number of times while parked, which drains the battery. If you’ve ever noticed clunks coming from the Mach-E while parked, this is the car waking up and using 12V battery (perhaps because you brought a fob or PAAK nearby). Short and infrequent trips also cause increased 12V issues since there is not enough ON time to recharge the 12V battery completely.

Hardwired dashcams, 3rd party apps accessing vehicle data, and OBD-II adapters left plugged in are also common owner mistakes that cause drains and contribute to 12V issues.

What causes 12V drains?

Here are the most common causes:

• An improperly wired dashcam that stays on when the vehicle is off.
• 3rd party apps (such as Recurrent, Optiwatt, Tronity, ev.energy, Home Assistant, Homebridge, Utility smart charging app, etc.) that access vehicle or charging data 24/7. The pings from these apps wake up the car too often. Ford has mostly cracked down on this and will lock your account if they detect misuse.
• An OBD-II adapter left plugged in (except for OBDLink MX+, which has a low enough standby drain) or left active (always be sure to stop data collection and disconnect when done).
• Excessive welcome lighting activation from fobs or PAAK near the vehicle. Disable welcome lighting in vehicle settings, keep your fobs 25’ from the car, and quit/disable FordPass on your phone.
• A rodent has chewed some wires.

Will leaving something plugged into the 12V port drain the battery?

No. The 12V and USB ports shut off automatically a few minutes after the vehicle is turned off, so they are safe to use and will not cause a drain. Remember to avoid using accessory mode, if you want to use the ports turn the car fully ON.

What is sulfation?

Sulfation is the name of the process that occurs on the surface of the lead acid plates inside the battery when it’s discharged. The electrochemical reaction for discharge converts sulfuric acid electrolyte into solid lead sulfate, which coats the electrode plates in the cells. As the battery discharges more, the lead sulfate gets thicker. On flooded batteries, you can actually see the sulfation on the plates if you opened the cell caps on a discharged battery (it looks like an off-white plaque).

Charging the battery reverses this condition, lead sulfate goes back to sulfuric acid. However, if the battery has been left in a discharged state for a long time (weeks or months) this sulfation plaque can become hardened and will not go away easily. This is why chronically undercharged batteries (that spend most of their time below 60%) can be difficult to recharge and may have reduced capacity. The only way to fix this in an AGM is with extended duration charging (called desulfation or reconditioning). Depending on severity, it can take days or weeks to desulfate a battery. For more information, see my separate topic: How to Recondition/Service Your 12V Battery

How do cold temps affect the 12V battery?

Cold slows down the rate of chemical reactions. This means your battery takes longer to charge, and also can’t supply power as fast. It will also lose capacity in the cold just like the high voltage battery. At 5ºF, the 12V battery is down to only 50% capacity.

The cold can particularly affect OTA installations. The battery has less capacity available to install updates, and it takes much longer to charge up to the required level. So cold becomes a double whammy for OTAs.

Extreme cold can also cause the 12V battery to freeze. See below.

Can the 12V battery freeze?

Yes, if it is discharged and cold enough. A fully charged AGM can withstand -75ºF. But the freezing point of the electrolyte increases as the battery is discharged. If the battery is discharged to 40% SoC, the electrolyte will now freeze at +5ºF. In other words, discharged batteries can freeze. AGMs are starved of electrolyte and are more resistant to freezing than flooded batteries, but they can still freeze. When a battery freezes, it will cease to function, cannot be charged, could be permanently damaged, and could split open. This is why it’s important to keep lead acid batteries fully charged in extreme cold weather.

I now have answers to questions I had, and didn't have (yet). Comprehensive great information that will prevent me from doing some stupid things, and help prevent having a problem in the future. Thank you so much for sharing this information. Happy New Year.

 

[dpnelson]

How much is the 12V battery drained each time the MME wakes up?
I went to the bottom of this because I suspected that repeated wake-ups events might be the reason why my Mach-e is destroying a 12V battery in just 6 months. The bottom line is that that indeed appears to be the main problem. I measured the true 12V battery current using a professional amp meter.

When does the car wake up?, and what does it do?
The MME wakes up when the keypad is touched, the lock button is pushed on the key fob or when it connects via bluetooth using PAAK. Rather than going to sleep quickly, the insomniac car stays awake for much longer than expected after that. I measure that it drains about 11 Amps (132 Watt) for 3 minutes and after that ~3 Amps (36 Watt) for another 15 minutes. No lights are on during that time. Then it finally goes back to sleep.

This means that each wake-up event uses ~1.25 Ah, or about 3.5% of the available energy in the 35Ah 12V battery. If the car starts out at a healthy 85% State-of-Charge and it is woken up 10 times without starting it, the battery would have drained down to 50%. AGM batteries should not be drained much lower.

Things are much worse with PAAK!
After wake-up and the initial 3-minutes of 11Amps heavy drain, I measure that the MME continuously drains ~6 Amps for as long as the phone is connected to the car via BlueTooth with the FordPass app. I left it on for 45 minutes but it did not go to sleep until I switched off the Bluetooth on my phone.

Why is this a problem?
The unnecessary drain adds significant wear to the tiny 12V battery. It will need to recharge each time, reducing range. I am on my 3rd battery already. The MME will automatically recharge the 12V battery whenever its SoC gets too low (probably 50%), so this will unlikely brick the car immediately. A weak battery, however, prevents OTA updates and results in nebulous warning messages.

When is it a problem?
The car wakes up each time the phone with PAAK gets within 30 feet. Since my garage is attached to the house, it is not unlikely that it wakes up many times when I wander through the house, take out trash or otherwise get anywhere within 30-40 feet. If I leave my phone at my desk, it is not unlikely that it will continuously connect to the car as that is ~30 feet from the car.

The regular key fob does not have this problem because that does not wake up the car until a button is pushed. PAAK - on the other hand - secretly wakes up the entire car without user action.

What would help?
Obviously, not using PAAK, or parking the car farther away to avoid accidentally waking up the MME. It appears that PAAK is poorly implemented. At the very least Ford could update the software to make the car go to sleep much quicker. There truly is no reason to keep the car awake for 15 minutes after each event. 2 minutes would more than be enough. And there is no reason to drain this much energy while being awake while locked. Note that the car also stays awake for 15 minutes each time after the car is locked.

How was the 12V battery drain measured?
To avoid 'Heisenberg issues' I measured the actual current contactless using a DC clamp multimeter at the negative 12V battery lead. It is easy to do. I verified that the current matched the data from an OBDII dongle running CarScanner (the MME measures current at the positive lead). Here is the meter reading 6.1 amp while FordPass is connected using bluetooth but the car is still locked.

In addition to things going back to sleep slowly, 132 watts is quite a lot of power for something that shouldn't be doing anything mechanical. I suspect a lot of the modules that power up are carryovers from internal combustion vehicles. They probably use very old semiconductor processes and lack low power modes since a few watts here and there don't really matter on a traditional car with a much larger battery.

 

[Lineareagle]

Excellent. So I assume using Ford Pass to check my charge is causing a wake up?
As well can a metal box in the garage to put the fob in when I come home sufficiently stop the car from waking up? I often go into the garage with the fob in my pocket to do work, bad idea?

 

[kennan]

Lee you the goat for this thread, thank you & bookmarked

 

[Maquis]

Excellent. So I assume using Ford Pass to check my charge is causing a wake up?
As well can a metal box in the garage to put the fob in when I come home sufficiently stop the car from waking up? I often go into the garage with the fob in my pocket to do work, bad idea?

There’s no reason to check your charge unless you’re charging and the 12VB is being charged while the car is charging.

I leave my fob in the car or the garage. Never had an issue. The car will only wake up when an out-of-range fob is brought in range.

 

[Ride_the_lightning]

you might want to add something along the lines that

'all doors MUST be closed to have the DC_DC continue to power the 12v battery. Otherwise, the inverter/load will drain the 12v battery rapidly'

What???? So tailgating with my car ON will drain my 12V battery? Wtf Ford? What could possibly be the reason for disabling the DC/DC converter when the door is opened?

 

[Lineareagle]

There’s no reason to check your charge unless you’re charging and the 12VB is being charged while the car is charging.

I leave my fob in the car or the garage. Never had an issue. The car will only wake up when an out-of-range fob is brought in range.

Good to know:

 

[Shayne]

Fordpass feature request.

 

[Ride_the_lightning]

What???? So tailgating with my car ON will drain my 12V battery? Wtf Ford? What could possibly be the reason for disabling the DC/DC converter when the door is opened?

So I just checked this with my OBD reader. Opening the door drops the DC voltage from about 14.7 down to 13.3. The DC-DC converter initially drops down to 0 amps, but then immediately ramps back up after a few seconds. It indeed seems to be dropping the voltage to stop charging the 12V battery, but the DC-DC converter seems to keep powering everything else in the car. It shouldn’t drain the battery to have the doors open (which is consistent with my 2 years of use. I’ve left the doors and rear hatch open a lot).

 

[RobbertPatrison]

How much is the 12V battery drained each time the MME wakes up?
I went to the bottom of this because I suspected that repeated wake-ups events might be the reason why my Mach-e is destroying a 12V battery in just 6 months. The bottom line is that that indeed appears to be the main problem. I measured the true 12V battery current using a professional amp meter.

When does the car wake up?, and what does it do?
The MME wakes up when the keypad is touched, the lock button is pushed on the key fob or when it connects via bluetooth using PAAK. Rather than going to sleep quickly, the insomniac car stays awake for much longer than expected after that. I measure that it drains about 11 Amps (132 Watt) for 3 minutes and after that ~3 Amps (36 Watt) for another 15 minutes. No lights are on during that time. Then it finally goes back to sleep.

This means that each wake-up event uses ~1.25 Ah, or about 3.5% of the available energy in the 35Ah 12V battery. If the car starts out at a healthy 85% State-of-Charge and it is woken up 10 times without starting it, the battery would have drained down to 50%. AGM batteries should not be drained much lower.

Things are much worse with PAAK!
After wake-up and the initial 3-minutes of 11Amps heavy drain, I measure that the MME continuously drains ~6 Amps for as long as the phone is connected to the car via BlueTooth with the FordPass app. I left it on for 45 minutes but it did not go to sleep until I switched off the Bluetooth on my phone.

Why is this a problem?
The unnecessary drain adds significant wear to the tiny 12V battery. It will need to recharge each time, reducing range. I am on my 3rd battery already. The MME will automatically recharge the 12V battery whenever its SoC gets too low (probably 50%), so this will unlikely brick the car immediately. A weak battery, however, prevents OTA updates and results in nebulous warning messages.

When is it a problem?
The car wakes up each time the phone with PAAK gets within 30 feet. Since my garage is attached to the house, it is not unlikely that it wakes up many times when I wander through the house, take out trash or otherwise get anywhere within 30-40 feet. If I leave my phone at my desk, it is not unlikely that it will continuously connect to the car as that is ~30 feet from the car.

The regular key fob does not have this problem because that does not wake up the car until a button is pushed. PAAK - on the other hand - secretly wakes up the entire car without user action.

What would help?
Obviously, not using PAAK, or parking the car farther away to avoid accidentally waking up the MME. It appears that PAAK is poorly implemented. At the very least Ford could update the software to make the car go to sleep much quicker. There truly is no reason to keep the car awake for 15 minutes after each event. 2 minutes would more than be enough. And there is no reason to drain this much energy while being awake while locked. Note that the car also stays awake for 15 minutes each time after the car is locked.

How was the 12V battery drain measured?
To avoid 'Heisenberg issues' I measured the actual current contactless using a DC clamp multimeter at the negative 12V battery lead. It is easy to do. I verified that the current matched the data from an OBDII dongle running CarScanner (the MME measures current at the positive lead). Here is the meter reading 6.1 amp while FordPass is connected using bluetooth but the car is still locked.

I am still chasing a root cause of 12V battery drain. Just now it drained from 92% TO 72% overnight. That is a 20% drop: 84Wh lost from a small 35Ah battery. To be sure, I had unplugged my dashcam, though that does not seem to make any difference as the USB outlets are unpowered when the vehicle is off. On another occasion I measured 10% drop in 2.5 hours. That works out to a load of ~20watt (1.7A) continuous, in the ballpark of what I measured with the clamp multimeter at the battery terminal. This car has insomnia....

The constant discharging and recharge sneakily wears out the 12V battery. I get no messages about battery drain, so the car thinks this draw is from its normal operation. It is just that the 12V battery will die after 6-12 months. This is my 3rd one.

Plugging in the car only helps a little. It charges the 12V battery only while the main battery is charging. So after HVB charge is completed the 12V battery still discharges while plugged in.

Measured at the battery terminal, the drain goes up and down, so this does seem to be a software issue. The problem appears to be less when I switch off Bluetooth on my phone to silence PAAK. The car parked in the garage triggers some wake up events, but disabling PAAK does not fully avoid the problem. I wonder what else could cause this. Any ideas?

 

[Ride_the_lightning]

I am still chasing a root cause of 12V battery drain. Just now it drained from 92% TO 72% overnight. That is a 20% drop: 84Wh lost from a small 35Ah battery. To be sure, I had unplugged my dashcam, though that does not seem to make any difference as the USB outlets are unpowered when the vehicle is off. On another occasion I measured 10% drop in 2.5 hours. That works out to a load of ~20watt (1.7A) continuous, in the ballpark of what I measured with the clamp multimeter at the battery terminal. This car has insomnia....

The constant discharging and recharge sneakily wears out the 12V battery. I get no messages about battery drain, so the car thinks this draw is from its normal operation. It is just that the 12V battery will die after 6-12 months. This is my 3rd one.

Plugging in the car only helps a little. It charges the 12V battery only while the main battery is charging. So after HVB charge is completed the 12V battery still discharges while plugged in.

Measured at the battery terminal, the drain goes up and down, so this does seem to be a software issue. The problem appears to be less when I switch off Bluetooth on my phone to silence PAAK. The car parked in the garage triggers some wake up events, but disabling PAAK does not fully avoid the problem. I wonder what else could cause this. Any ideas?

Have you tried fully turning off all connected services in the car? Maybe something is causing the ford servers to ping the car way too often. This would at least see if it’s a network-related module causing the drain.

 

[RobbertPatrison]

Have you tried fully turning off all connected services in the car? Maybe something is causing the ford servers to ping the car way too often. This would at least see if it’s a network-related module causing the drain.

Good suggestion! Ok, that will be my next experiment. It might be that FordPass is polling the car often via the cellular network. Turing off all connected services should disable that.

 

[Mach-Lee]

What???? So tailgating with my car ON will drain my 12V battery? Wtf Ford? What could possibly be the reason for disabling the DC/DC converter when the door is opened?

That comment isn't factual, the DC/DC stays on as long as the ignition is ON regardless of door open. Voltage may change, but it stays on. Don't use accessory mode while tailgating to avoid 12V drain per the FAQ.

I am still chasing a root cause of 12V battery drain. Just now it drained from 92% TO 72% overnight. That is a 20% drop: 84Wh lost from a small 35Ah battery. To be sure, I had unplugged my dashcam, though that does not seem to make any difference as the USB outlets are unpowered when the vehicle is off. On another occasion I measured 10% drop in 2.5 hours. That works out to a load of ~20watt (1.7A) continuous, in the ballpark of what I measured with the clamp multimeter at the battery terminal. This car has insomnia....

The constant discharging and recharge sneakily wears out the 12V battery. I get no messages about battery drain, so the car thinks this draw is from its normal operation. It is just that the 12V battery will die after 6-12 months. This is my 3rd one.

Plugging in the car only helps a little. It charges the 12V battery only while the main battery is charging. So after HVB charge is completed the 12V battery still discharges while plugged in.

Measured at the battery terminal, the drain goes up and down, so this does seem to be a software issue. The problem appears to be less when I switch off Bluetooth on my phone to silence PAAK. The car parked in the garage triggers some wake up events, but disabling PAAK does not fully avoid the problem. I wonder what else could cause this. Any ideas?

Have you used any 3rd party apps in the past that access vehicle data? Think hard. Here’s the list: Optiwatt, Recurrent, ev.energy, ABRP (OTA live data), Tronity, Charge Smart MA, SmartCharge Rewards, other power utility control/saver apps, FordPass plugins for HomeBridge or Home Assistant, phone widgets.

If so, you need to change your FordPass password to rule out polling.

I would not disable connected vehicle data completely, you won’t get OTAs and BlueCruise will stop working. Fix the root cause of the polling instead.

 

[RobbertPatrison]

That comment isn't factual, the DC/DC stays on as long as the ignition is ON regardless of door open. Voltage may change, but it stays on. Don't use accessory mode while tailgating to avoid 12V drain per the FAQ.


Have you used any 3rd party apps in the past that access vehicle data? Think hard. Here’s the list: Optiwatt, Recurrent, ev.energy, ABRP (OTA live data), Tronity, Charge Smart MA, SmartCharge Rewards, other power utility control/saver apps, FordPass plugins for HomeBridge or Home Assistant, phone widgets.

If so, you need to change your FordPass password to rule out polling.

I would not disable connected vehicle data completely, you won’t get OTAs and BlueCruise will stop working. Fix the root cause of the polling instead.

I'm happy to try everything. If brute-force switching off connected vehicle services indeed shows a difference, then polling over the cellular network is the problem indeed.

The only thing I can think not is having FordPass running on both my iPhone and an Android phone at the same time. I am not sure why that should dramatically increase polling, but it could. We will see.

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