How to Recondition/Service Your 12V Battery

[Mach-Lee]

FYI fully charged voltage on an AGM is 12.8-12.9V (it’s higher than a flooded battery). Check after the battery has been sitting for at least 3 hours, and without waking up the car.

Here’s a generic SoC chart for AGMs:

AGMs in excellent shape will hold over 13V for about a day after charging with no loads.

Also, open circuit voltage isn’t a great indication of sulfation level (SoC only). Float current is the best way I’ve found. Charge till the milliamps stop decreasing.

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[generaltso]

Charge till the milliamps stop decreasing.

What do you use to measure the DC current down that low? I have a clamp meter, but I don‘t think it can measure DC below 1A.

 

[dtbaker61]

My quick check (I added the port plugs, one of the best mods yet!) yesterday afternoon measured 12.1 V.

hhhmmm, that does NOT sound good...

are you willing to 'test' your on-board charge system and then re-measure resting voltage? you' dbe the perfect candidate to test whether the on board system can perk up the LVB.

- park
- turn MME on
- turn 'auto-timeout' setting OFF
- leave MME 'on' overnight
- turn MME 'off', pop the hood, turn off your BT
- wait an hour
- sneak up on MME without waking it up, and measure LVB voltage

 

[dtbaker61]

FYI fully charged voltage on an AGM is 12.8-12.9V (it’s higher than a flooded battery). Check after the battery has been sitting for at least 3 hours, and without waking up the car.

Here’s a generic SoC chart for AGMs:

AGMs in excellent shape will hold over 13V for about a day after charging with no loads.

Also, open circuit voltage isn’t a great indication of sulfation level (SoC only). Float current is the best way I’ve found. Charge till the milliamps stop decreasing.

our *very small* AGM LVB may have a slightly different resting voltage with such little internal plates.... I wouldn't be too surprised to find out that 12.6-12.8 was 'ok'. Less than 12.6 probably is NOT ok as a resting voltage unless there are some significant background loads we don't know about

 

[Mach-Lee]

What do you use to measure the DC current down that low? I have a clamp meter, but I don‘t think it can measure DC below 1A.

Hook up a multimeter in series with the charger, but you'll have to limit current to 5-10A on the supply to avoid blowing the multimeter fuse. I charge with a bench power supply that reads out the current. Measuring the current is nice, but don't worry about it too much if your setup is getting too complicated.

our *very small* AGM LVB may have a slightly different resting voltage with such little internal plates.... I wouldn't be too surprised to find out that 12.6-12.8 was 'ok'. Less than 12.6 probably is NOT ok as a resting voltage unless there are some significant background loads we don't know about

Voltage has nothing to do with plate size. It has to do with the specific gravity of the electrolyte. AGMs use a "hotter" mix of sulfuric acid than flooded batteries.

12.6V is about 80% charged on an AGM.

 

[dtbaker61]

What do you use to measure the DC current down that low? I have a clamp meter, but I don‘t think it can measure DC below 1A.

most chargers are set up with internal charge curves that are temperature compensated, and a % of the amp-hr capacity of the battery (the C rate).

most DIY quality clamp ammeters are not super accurate... the internal one probably is pretty dang good. The factory charge curve, shunt, and firmware/software has probably been pretty carefully set to match the exact battery used... which is part of why it would be a bad idea to change chemistry or size.

The big questions are what the resting v of our LVB should be (and how to set up correct test conditions), how to get the onboard system to effective charge it fully, and how to 'prove' it is not working to the Dealership if it isn't so we can get it squared away by Ford under Warranty

 

[louibluey]

hhhmmm, that does NOT sound good...

are you willing to 'test' your on-board charge system and then re-measure resting voltage? you' dbe the perfect candidate to test whether the on board system can perk up the LVB.

- park
- turn MME on
- turn 'auto-timeout' setting OFF
- leave MME 'on' overnight
- turn MME 'off', pop the hood, turn off your BT
- wait an hour
- sneak up on MME without waking it up, and measure LVB voltage

Sure, but I put it on the charger this afternoon, so it may or may not still be a good test, but certainly game in days to come.

Two days in a row when I checked 12.1 V, but I had the FOB, so maybe that complicates things. So, maybe it should be left unlocked and approach with no FOB and no phone (no BT nearby)?

 

[louibluey]

FYI fully charged voltage on an AGM is 12.8-12.9V (it’s higher than a flooded battery). Check after the battery has been sitting for at least 3 hours, and without waking up the car.

Here’s a generic SoC chart for AGMs:

AGMs in excellent shape will hold over 13V for about a day after charging with no loads.

Also, open circuit voltage isn’t a great indication of sulfation level (SoC only). Float current is the best way I’ve found. Charge till the milliamps stop decreasing.

Now I'm intrigued. Tempted to just buy another one if I can find it, put the new one in the MME, then play with this one in the lab.

 

[dtbaker61]

Now I'm intrigued. Tempted to just buy another one if I can find it, put the new one in the MME, then play with this one in the lab.

what is really a wild card is the 'voltage sag' with temperature and/or loads. With a relatively small battery like our MME LVB.... even 'small' loads will pull down the voltage. So anything that 'wakes up' the computer, security, puddle lights, Frunk light might be pulling the LBV voltage down considerably.... until the MME is 'on' and the onboard dc-dc feeds it.

The most accurate read would probably require having the MME 'on' for several hours, park, and disconnect the LVB so there are NO loads, let it settle, and then measure

 

[generaltso]

The most accurate read would probably require having the MME 'on' for several hours, park, and disconnect the LVB so there are NO loads, let it settle, and then measure

I didn't disconnect the battery, but I left the hood open and let it sit for about 4 hours and got a measurement of 12.7V. That looks like it equates to about 85%.

 

[louibluey]

Supposedly Rock Auto has one genuine Motorcraft BHAGM-H3 for $168 with FedEx ground $9 shipping, with tax around $194. That's probably cheaper than I can get a local Ford parts counter, if they have any. Wild card is if FedEx can get it here in one piece, or if they really still have one.

Probably should have used my PL 6100, but it is still new, and with the 60A charge capability, don't trust it yet to run unattended overnight. The little one has run for days, worst problem is it shut off a couple of times. Checked it, now reading 13.6V and the yellow light is blinking which I think is part of the cycling. I think it said 40% charge when I started it, a good sign that seems to agree with 12.1V on the graph above.

Funny, past EVs I have been hesitant to connect any kind of power supply or charger for concern over upsetting or damaging some electronics. But, having the FDRS experience now where chargers or power supplies are routinely used, plus seeing the DC-DC converter up to 15V now, I am less concerned. I also agree that none of this should be necessary, but there seem to be at least minor problems, and looking into it is kind of fun, plus I guess I am about to learn a little about AGM batteries.

It will be a lot easier to look at this one in the lab, all sorts of hp and Agilent power supplies and instrumentation. My FE was built Dec 20, and the dealer got it Feb 21, plenty of time for 12V damage, plus I had the 12V discharge problem too.

 

[louibluey]

This morning, the charger was off, no idea if the charger thought it was done, or if a grid power glitch turned it off (seems more likely). Waking the charger (setting 10A) the charger volt meter showed 12.9V, not charging yet (another button press), 33 F unheated garage. Hood was already open as in the picture above, no fob or iPhone, I think MME did not wake.

Starting the charger (MME still dormant), the charger went right to 14.9/15.0 V. I would have been concerned, but for noticing the MME DC-DC converter has been doing 15.0 V lately (not sure if cold weather related, or the state of my 12 V LVB). I have been getting some LVB warnings on FordPass.

Hey, I guess Rock Auto really did have one left in stock, and they shipped on a holiday (or just printed the label).

I plan to try the @Mach-Lee milliamp test, and possibly some AC battery impedance tests in the lab. But, if these MME LVB are really unobtanium, and anyone has a critical need for a LVB in the upstate, NY area (assuming it arrives okay), you can have it at cost for local pick up. I am sure shipping is prohibitive, some dealer online sites were quoting shipping of $140!

 

[JimmyMachE]

Car Scanner ElmObd2 app shows the voltage and SOC of the Aux battery. There's even the standby drain in mA. Not sure how reliable these readings are, most other parameters seem ok.

 

[dtbaker61]

Car Scanner ElmObd2 app shows the voltage and SOC of the Aux battery. There's even the standby drain in mA. Not sure how reliable these readings are, most other parameters seem ok.

yeah, but MME has to be 'on' to power ODB, doesn't it? .... so it won't show the 'resting' voltage of the LVB...

 

[AlpaChino]

This guide would apply if you got a message about needing to service your 12V battery, 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 indicate your 12V battery is low. Charging the 12V battery fo an extended period may help solve these issues.

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 probably need to schedule service.

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 (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 15.0V 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. Check when the car is in sleep mode (all lights off, 30 minutes since opening a door or the hood). A value much below this means the battery is not fully charged.

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 14.9V in cold temps to avoid gassing.



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 when the car is off, so you shouldn’t have to do this unless you are experiencing low voltage issues.

Give this man a Pulitzer. This is an excellent write up that will be used for many years. Thank you.