How to Recondition/Service Your 12V Battery

[generaltso]

For those of us who are not engineers, when say turn the MME on, is that just the auxiliary mode or full on?

It has to be in Ready mode (full on).

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[dtbaker61]

For those of us who are not engineers, when say turn the MME on, is that just the auxiliary mode or full on?
I’ve had the LVB fault 2 days in a row. I want to try this.
Also, I have departure times set, but don’t hook up to a charger overnight. Will that cause this “fault?”

.... full on, like you are going to drive.... this energizes the on-board dc-dc converter that uses energy from the HV battery to run the 12v system (at 14.4-14.9 volts) which charges the little 12v AGM battery.

You do have to then go into Settings, and toggle OFF the 'auto-timeout' setting so the MME doesn't turn itself off after 10, or 30 minutes depending how you have it set.

Leaving the vehicle on 'several hours' or overnight will ensure that the little 12 battery gets fully charged; which might not be happening if you usually just take very short trips. But is might NOT won't if there is actually something wrong with your systems or 12 battery.

 

[PA Bob]

It has to be in Ready mode (full on).

Also, should I hook it up to my charger?

 

[dtbaker61]

Also, should I hook it up to my charger?

you don't really HAVE to, but it won't hurt, and will keep your HV battery up rather than discharging to keep the 12v system running.... which takes about 200 watts!

 

[bob b]

This guide would apply if you got a message about needing to service your 12V battery, electrical system drain, your car has gone into deep sleep mode unexpectedly, or are getting a ton of error messages when starting the Mach-E (low battery voltage will cause modules to shut down and/or produce errors). These error messages may indicate your 12V battery is low. Charging the 12V battery for an extended period and/or software updates may help solve some of these issues.

Oct 2022 Update - See below for common causes of 12V errors:

Using 3rd party apps or widgets that access vehicle data through your FordPass account may cause 12V battery drains. These apps could be designed to monitor vehicle status (widgets), smart charging (Optiwatt, ev.energy), battery heath (Recurrent), or utility charging control or saver programs (Charge Smart MA) that directly control your Mach-E charging through your Ford account. Excessive data polling by these apps causes the vehicle to stay awake in some cases. If you are having 12V drain issues, I suggest you remove access to your FordPass account through these apps and delete them to see if the problem goes away (remove your vehicle from their server, don't just delete the app). Changing your FordPass password will also help revoke access.

Hardwired dashcams may also cause 12V drains. Dashcams should only use switched power so they shut down a few minutes after the car is shut off. Rewire you dashcam if it stays on when the car is off (do not use parking mode).

Welcome lighting can be repeatedly triggered when you are parked within range of the key fob or PAAK (e.g. at home) and can sometimes cause a battery drain afterwards. This affects some vehicles differently than others for unknown reasons. Walking around near the fob or car can cause changes in received signal strength that make the car think you are approaching (even when nothing is moving). I recommend disabling welcome lighting as a potential cause if you experience a 12V drain message as part of your troubleshooting.

Charging faults (amber/red ring flashing on the charge port) can also cause the 12V battery to drain since the car will enter an error state. The 12V battery will not be maintained in the charge error state. Address these charging issues with your dealer ASAP. You may need a new EVSE, software updates and/or a new charge port to fix charge errors. I recommend recharging the 12V battery if you got a 12V fault message after experiencing a red ring error.

OBDII adapters plugged into the data link connector under the dash may keep the vehicle CAN buses active in some cases. This can prevent the car from going fully to sleep. Unplug these devices when the vehicle is parked as part of your 12V drain troubleshooting.

If your vehicle is in for service, technicians frequently operating doors, leaving them open, or leaving the car in Accessory mode (to use the radio) may cause the battery to drain and trigger a warning. Sometime you may see a warning a day or two after service. In this case there is no concern, drive and charge the vehicle normally for a few days and the battery should return to normal.

Some vehicles may have a faulty High Voltage Battery Junction Box (HVBJB), which causes a large 12V battery drain when a stop safely now fault occurs. Failure of a HV contactor to actuate will cause an inability to recharge the 12V battery. Turn the car completely off to save the battery and call a tow truck if this happens. Ford has released recall 22S41 for this issue, improved fault handling allows the vehicle to maintain 12V power and continue operating in a reduced power mode.

Failed OTA attempts may also cause a 12V drain in some rare circumstances. Please contact Ford for assistance.

12V Battery Fault - Service Soon - This error message in FordPass means that the 12V battery has reached a low level and was automatically recharged while the car was turned off (not a normal occurrence). This is not an urgent concern, more so an advisory that the battery was run down lower than normal operating range. It does not mean your battery has to be replaced. It may just be a software glitch or due to doors being left open during service work. I would ignore this message the first time you see it, but if it happens again I would advise you follow the charging steps below one time. You are more likely to see this message during cold weather since the battery capacity is more constrained by the cold.

Stop Safely Now/Full Accessory Power Active - This error combo usually means the 12V battery is almost dead and can't start the car, and you are likely stranded. If this happens, completely turn off the vehicle to preserve the battery until help arrives. Jump start from another running vehicle if possible using the jumper posts (access instructions below in video). Portable jump packs will not work because they don't have enough power. Alternately, disconnect the negative battery terminal and charge the 12V battery with a charger for several hours before trying again. You must disconnect the battery when using a charger less than 20A, otherwise the car will steal all the power from the charger trying to repeatedly start the modules in the vehicle and the battery won't actually charge. Complete a full duration 24-48 hr charge when you are back home after this happens to recondition the battery.

Additionally, I recommend a 12V charging session for all newly delivered vehicles since they’ve been sitting for extended periods during shipment (typically a month or more). This will ensure optimal battery health as you start ownership. Some vehicles are being delivered with an extremely low HV battery state of charge (SoC) and dead 12V batteries (the 12V battery is no longer maintained at low SoC, so it dies). Batteries that have gone completely dead in shipment will need a servicing charge detailed in this guide, or replacement under warranty.

To address these issues, I recommend charging the 12V battery for several days to fully restore its condition. This is an optional one-time procedure, read on for details. Charging may be a simple fix that would save you a dealer trip or battery replacement, but if issues return after charging you will likely need to schedule service. A significant number of battery issues appear to be caused by bad software or hardware, as many Mach-E batteries test fine after they are fully charged after an incident.

Disclaimer: Not all batteries can be saved with this method, some will still require replacement if issues return.

Note: The 12V battery is maintained by the charging system under normal use. This procedure is not necessary unless you are experiencing the weak-battery issues referenced above.

Background

The 12V battery is located in the front trunk (frunk) and is separate from the high voltage battery. It’s a little different than a traditional car battery, it’s much smaller (only 35 Ah) and an AGM type. AGM stands for Absorbed Glass Mat, which mean the electrolyte is sealed inside and is non-spillable. AGMs charge slightly differently and can have some specific problems compared to regular flooded lead acid batteries, which we’ll consider with our charging strategy.

AGMs can charge very quickly up to about 80%, but the last 20% can be very slow (takes several hours). Because of this, AGM batteries are actually more likely to have a condition called sulfation caused by chronic undercharging, which can significantly reduce battery performance. When a lead acid battery discharges, the sulfuric acid in the electrolyte combines with the lead to form lead sulfate (a solid) on the surface of the plates. This coating of sulfate gets thicker as the battery discharges, blocking access to the lead plate below. This is called sulfation. When the plate is completely coated, the battery is dead. Charging reverses this process and converts the lead sulfate back into sulfuric acid, restoring access to the lead plates.

If the battery sits for a long time in a discharged state, more than a week or two (such as in a factory lot, or during shipment to a dealer), the lead sulfate becomes “hardened” with age and gets increasingly difficult to remove. Charging won’t remove all of it right away, so the battery performance suffers. Therefore, it’s important to always keep lead acid batteries fully charged so there is no sulfation present in the battery.

There are a lot of tricks out there for desulfating batteries (including special chargers, adding chemicals, etc.) but most of these aren’t compatible with AGM-type batteries because they’re sealed shut (there are no caps to open). Your only option is to charge the battery for an extended period of time, because old sulfation takes a long time to remove (days or weeks), so that’s what we’re going to do.

The reason we have to provide extra charging is because the DC/DC converter (like an alternator) runs at a lower voltage with the car is on, and only runs intermittently when the car is off. If the battery is sulfated, it might not run long enough to charge the battery back up to 100% and clear out all the sulfation. This is especially true if you only drive short trips or use the vehicle occasionally rather than daily. Intermittent charging is fine for a good battery, but a sulfated battery will never be able to “catch up” and the sulfation will just become more ingrained with time. This will eventually lead to battery failure, possibly leaving you stranded. This is why it’s a good idea to proactively charge the 12V battery when you start having issues.

Correct voltage is important for AGM charging. Most two cycle chargers will charge to 14.4-14.7V during absorption mode, and switch to 13.5-13.8V during float mode. Charging at 15V or more (this is called equalization charging) will cause gas production (H2 and O2) in the cells. Normally an AGM is sealed, but excessive gas pressure will be vented under these conditions. When gas is vented from an AGM, it is a permanent loss of water from the cells and should be avoided to prevent the cells from drying out too much. You should only charge above 15V when the battery is known to have severe sulfation and limit the duration to minimize gas loss. Some chargers have modes that do >15V, so be cautious about using them. Charging at a lower (float) voltage for a much longer time is usually much more effective and is safer for the battery.

Charging

The battery needs to be charged by some method for at least 24-48 hours to have a chance at removing the more stubborn sulfation. Longer is better, in some cases it will take a week or two of continuous float charging to fully remove. I will cover several different methods.

WARNING: DO NOT USE RECONDITION/REPAIR/EQUALIZE MODE ON YOUR CHARGER, these can damage your AGM battery due to high voltage. Use regular AGM mode only. See below.

NOTE: a fully charged AGM will have an open circuit resting voltage of 12.85V or higher. A value much below this means the battery is not fully charged. Ford recommends a full recharge when the resting battery voltage is below 12.3V. Check when the car is in sleep mode (all lights off, 30 minutes since opening a door or the hood).

Battery Charger Method:

The easiest method is to use a regular automatic battery charger that has a float mode. Preferably it should have an AGM mode, if not it will just take a little longer. DO NOT USE A DUMB CHARGER that must be manually turned off. Remove the frunk covers to access the 12V jump points:


Video by Benjamin Kegele

Connect the battery charger to the + and – jump terminals shown in the video. Do not connect directly to the negative battery terminal, as this will bypass the battery current sensor and cause module shutdowns. Set the charger to the appropriate current for a car battery (10-20A recommended), and select AGM mode if available (see warning above about other modes). Leave connected for at least 24-48 hours. Note: some chargers may display fully charged once absorption mode is reached, when in fact the battery is only 80% charged at this point. It’s important to leave the charger connected after this indication for some time to fully remove sulfation.

To answer some FAQ’s about battery chargers, yes a charger without an AGM mode will still work. They just use a slightly lower voltage, so it will take a little bit longer to achieve the same result. Pulse desulfation chargers (such as BatteryMINDer) are also great, just use the regular charging mode as previously explained. Battery maintainers are also fine as long as they are “smart” and have separate charge and float stages. Maintainers are slower to initially charge the battery, so make sure it spends at least 24 hours in maintenance mode to make headway.

EDIT: Some battery chargers, such as the NOCO Genius, completely shut off the output as a power saving measure after the battery is fully charged. These types of chargers will not work for long-term desulfation, continuous voltage output is required. The charger must have a continuous float feature.

If you need to drive the car, just disconnect the charger and put it back on when you get home until you’ve gotten in your charging time. You can drive with the covers removed with no major issues, things might just get a little wetter if it rains.

Power Supply Method:

For fellow nerds with bench power supplies, this is the preferred method so you can monitor and optimize the charging process. The best method is a 3-stage CC, CV, CV profile:

Set your supply to 14.5V at max amps and let it charge in CC (bulk stage). Check on it every hour and try to make a note of when it switches to CV at 14.5V (absorption mode). You can leave it at 14.5V timed for up to 6 hours, or monitor the current drop. When the current drops below 1A or 6 hours have elapsed, lower the voltage to 13.6V (float mode) and let it sit for as long as you can. The battery is done desulfating when the float current stops decreasing. This could take a day or several weeks. A battery in great shape will have a float current less than 0.1% of its C rating (<35 mA for the Mach-E 35 Ah battery). For comparison, I had an AGM sitting around at 75% SoC that hadn’t been charged for a year or two, it took about 5 days of floating to reach a current minimum. Last little bit is very slow.

A note on temperature, the above voltages are for standard 25ºC/77ºF conditions. If it’s significantly hotter or colder than that in your garage you should adjust the voltage some. This is called temperature compensation, the adjustment constant is -0.024 V/ºC difference from 25ºC. So at 35ºC/95ºF your absorption voltage should be 14.26V. Do not exceed 15.2V in cold temps to avoid gassing. If at any time you hear high-pitched squeaking/farting noises coming from the battery, immediately reduce voltage as venting is occurring.

The below test was performed on a brand new BHAGM-H3 battery that appears to be about 6 months old, arrived at 12.83V (95% SoC). Power supply set at 13.60V, a current minimum of 14 mA was reached after about 24 hours maintenance charging as you can see below. Older or sulfated batteries will take longer than 24 hours to reach current minimum. The open circuit voltage after sitting 24 hours was 13.08V. The battery was then capacity tested and produced 43 Ah (35 Ah rated).

Congratulations, you’ve now desulfated your battery so it will perform better. If you still have issues and you have an early build car, have your dealer perform TSB 21-2091 to update the powertrain modules, there was a bug that caused the 12V battery not to charge that is now fixed. If you have the latest software and still have issues, your dealer may need to replace your 12V battery as they can go bad.

I want to emphasize this is an optional one-time procedure meant to help restore your 12V battery if it’s been sitting at a low charge. Under normal use the 12V battery should be maintained automatically, so you shouldn’t have to do this unless you are experiencing low voltage issues.

Hi, thanks for info. I have a c-tek battery trickle charger that I plug into my other car, it has a 12 volt cigarette lighter socket that plugs in inside the car. Can I use this on the mach-e and plug in at 12 volt acc socket inside mach-e instead of attaching under hood of car

 

[generaltso]

Hi, thanks for info. I have a c-tek battery trickle charger that I plug into my other car, it has a 12 volt cigarette lighter socket that plugs in inside the car. Can I use this on the mach-e and plug in at 12 volt acc socket inside mach-e instead of attaching under hood of car

No, that won’t work. The 12V socket turns off after a bit.

By the way, you may not want your complete home address listed in your profile.

 

[bob b]

thanks for advice, address has been deleted. concerning the use of 12 volt socket inside car for trickle charging, what if I go into mache screen settings and turn off automatic timeout setting, will socket stayed powered up then so I can use it ? thanks for your help.

 

[generaltso]

what if I go into mache screen settings and turn off automatic timeout setting, will socket stayed powered up then so I can use it ? thanks for your help.

The automatic timeout setting is for the car turning off if it’s left on. It doesn’t stop the 12V socket from turning off after the car is turned off.

 

[Mach-Lee]

Hi, thanks for info. I have a c-tek battery trickle charger that I plug into my other car, it has a 12 volt cigarette lighter socket that plugs in inside the car. Can I use this on the mach-e and plug in at 12 volt acc socket inside mach-e instead of attaching under hood of car

No, they shut off as generaltso also mentioned. The only option that doesn't involve opening the hood is to use an OBDII charging adapter cable like this:

https://www.amazon.com/dp/B007KJ2RZK/

However there is a strict 3 AMP MAXIMUM when using it, or you'll damage the car's wire harness. Do not use unless your charger is 3 amps or less! CTEK is NOT 3 amps or less and uses a different plug.

 

[dtbaker61]

thanks for advice, address has been deleted. concerning the use of 12 volt socket inside car for trickle charging, what if I go into mache screen settings and turn off automatic timeout setting, will socket stayed powered up then so I can use it ? thanks for your help.

if your MME is working correctly, you do NOT need a trickle charger at all. The MME monitors the 12v, checks periodically, and if it drops below about 12.1v, then MME wakes up.... turns on the dc-dc and charges your 12v battery from the HV battery.... and goes back to sleep.

 

[kennethjk]

The automatic timeout setting is for the car turning off if it’s left on. It doesn’t stop the 12V socket from turning off after the car is turned off.

Why can’t you just attach the c tek charge cables to the charge points under the beauty cover in the frunk

 

[generaltso]

Why can’t you just attach the c tek charge cables to the charge points under the beauty cover in the frunk

I assume he doesn‘t want to remove the covers.

 

[kennethjk]

I assume he doesn‘t want to remove the covers.

I have the holes drilled , one of the better recommendations on the forum, and there have been plenty.

 

[generaltso]

I have the holes drilled , one of the better recommendations on the forum, and there have been plenty.

So do I. But I’m guessing he doesn’t.

 

[jdhzzz]

Thanks for the post. It talked me off the ledge when I left the ODBII in it overnight. I hear tremendous thumping. Once the thumping stopped it was bricked. I read this, had an "Aha" moment, charged it, and it was back up in less than a day. Thank you, thank you, thank you.

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