How healthy is your 12v AGM battery ? [update to recommend replacing at 36mo]

[dtbaker61]

as I approached 36k miles and just passed 3 years of ownership.... I find myself wondering how long the 12v battery will perform adequately past 3-year warranty (assuming that your internal dc-dc and charging modules are working correctly to maintain the 12v battery).


[updated 6/4/24] - Be prepared to replace your 12v at 36mo, or shortly afterward. Things you may need to know so you don't get stranded:
https://www.macheforum.com/site/thr...r-12v-battery-recommended-at-36-months.36526/


I am hoping that the 12v batteries will last a LONG time since they are hardly ever 'deeply discharged' and never really have 'large loads' like turning over a starter motor. But, there is a risk of sulfation reducing capacity if you don't drive for months at a time or take only short trips that don't give time to fully charge the 12v and hold it at 100% for 'a while' to desulfate.

Our 12v batteries are probably hit the hardest by OTA downloads that last for 'a while' because the 12v battery cannot request a maintenance charge from HV during an OTA. If an OTA starts with your 12v at 80%, and it's a long OTA, it *could fail to finish* and leave your MME in a bad state, or even bricked in the 'inhibit' state.

Unfortunately, there is no absolute way to determine the state of health of your 12v battery.

At this point, I'd like to try and get some data from other owners willing to do some testing and log their results to this thread to see if we all can get a better idea of when it is time to replace the 12v.

----- 'leave-it-on' procedure to charge 12v to 100% ---------------

you will need an ODB2 reader, and an app like CarScanner to view 12v SOC%

- turn MME 'on'​

- disable 'auto-off' in vehicle>settings​

- turn headlights 'off'​

- turn HVAC 'off'​

​

...and leave the car on until 12v SOC hits 100%. This may take a day, or two, or three! If you end up driving somewhere in the middle it doesn't matter. As long as you leave the MME on, and lock doors from outside if needed.​

In my last 12v charge session, the first 24 hrs brought my LV up to 95%, second 24hr got it up to 100%. After 'sleeping' overnight undisturbed with the MME OFF, and Bluetooth OFF, I turned the car and bluetooth on and checked LV SOC via carscanner in the morning, and it had dropped to 86%. I don't know how that would compare to a NEW battery, but it is a data point for how a 40 month old 12v battery is holding up.

This may be the only way to get an idea of 'effective capacity remaining'; knowing that new=35ah... and seeing if 'remaining capacity' sleeping overnight after 100% charge changes over time.

------------------------------------------------------------------------
At this point I highly recommend either using a 12v charger, or a variable power supply, or leaving your MME 'on' once a month or so to get the 12v up to 100%. I'd be very interested to see more data from other people showing:

Batt_AGE (12c aux batt days since reset), Time_to_100%, SOC%_after8hrs

800 days, 48 hrs, 86% -------- my last measurement, what's yours ?!

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[markboris]

I’ve regularly replaced my batteries at 3 years which for me is usually about 45-50K miles. I do this because I never want to be stuck with a dead battery. I also might put more of a strain on them with front and rear cams, added amps for the audio system, lighting, etc. This Mach-E has the smallest battery I’ve ever had in a car and was kind of worried it wouldn’t even last three years but I’ve also never had an EV so not sure if the electrical and charging systems in this car are that much different than an ICE car. Not sure yet what I’m going to do but my three years is up at the end of this year.

 

[Monke]

I drove about 5k miles per year and the 12v battery was replaced at around 11 months. It could be a bad one.

 

[dtbaker61]

I’ve regularly replaced my batteries at 3 years which for me is usually about 45-50K miles. I do this because I never want to be stuck with a dead battery. I also might put more of a strain on them with front and rear cams, added amps for the audio system, lighting, etc. This MME has the smallest battery I’ve ever had in a car and was kind of worried it wouldn’t even last three years but I’ve also never had an EV so not sure if the electrical and charging systems in this car are that much different than an ICE car. Not sure yet what I’m going to do but my three years is up at the end of this year.

mmmmm, so you replaced yours on a schedule rather than upon failure or any indication of weakness.....

I am hoping that since EV 12v batteries do not 'do much', and are never under heavy loads such as turning an engine over, that they'll last a LOT longer as long as the internal dc-dc charger monitors and charges as expected.

 

[dtbaker61]

I drove about 5k miles per year and the 12v battery was replaced at around 11 months. It could be a bad one.

definitely sound like either a bad battery, or the internal dc-dc monitor/charging did not happen correctly.... perhaps exacerbated by relatively low use of 5k miles/year resulting in the vehicle not being 'on' long enough to keep the 12v charged.

 

[markboris]

mmmmm, so you replaced yours on a schedule rather than upon failure or any indication of weakness.....

I am hoping that since EV 12v batteries do not 'do much', and are never under heavy loads such as turning an engine over, that they'll last a LOT longer as long as the internal dc-dc charger monitors and charges as expected.

Yes, I've done this for years. Kind of like water heaters. I use to replace them once every 7 years whether they were leaking or not. I even replaced my HVBJB prior to it going bad and the recall coming out. I just don't like surprises or being stuck somewhere. I'm aware a battery can go bad at any time but I feel 3 years is a good run.

I do however agree with you in that there is much less demand on the one in the Mach-E. This is most likely why Ford was able to get away with such a small battery compared to an ICE car and the ones I am use to replacing.

 

[SpaceEVDriver]

I have typically replaced my flooded batteries with higher Ah AGMs within 3 years of getting the vehicle. After that, I typically don't have to touch the battery for five years or more.

My Lightning LVB is bulging on the sides and I don't have time to go to the dealer, so I ordered an H4 to use in place of the H3 if it fails on me while I'm away from home. I'll drive with the OEM battery until it fails.

My Mustang has its original battery with 38,000 miles on it. I don't have time to test its health right now, but will try to do that next week.

 

[MustangRio]

I just had mine replaced last month, at 56,000 miles and 38 months of ownership.

No warning either, just turned off my car one evening, and would not start the next morning.

 

[macchiaz-o]

Yes, I've done this for years. Kind of like water heaters. I use to replace them once every 7 years whether they were leaking or not.

That's a little different. I replace the anode rod and drain sediment roughly every 1.5-2.5 years, so that I can avoid replacing the entire water heater. I think the analogy here is to replace the battery ahead of need, rather than replacing the entire vehicle.

My dealer service department replaced my AGM battery at around 35 months (barely within warranty) because they tested it and confirmed that it was failing. They said it was even leaking acid, though I didn't see that myself and I know for sure the service advisor isn't always knowledgeable or honest with me...

But anyway, I suspected a dying LVB based on repeatedly failing OTA updates and the fact that the percentage reported on ford.com was generally around 40-60% instead of generally being around 80-90%, as measured by checking it daily for several weeks.

 

[dtbaker61]

I have typically replaced my flooded batteries with higher Ah AGMs within 3 years of getting the vehicle. After that, I typically don't have to touch the battery for five years or more.

My Lightning LVB is bulging on the sides and I don't have time to go to the dealer, so I ordered an H4 to use in place of the H3 if it fails on me while I'm away from home. I'll drive with the OEM battery until it fails.

My Mustang has its original battery with 38,000 miles on it. I don't have time to test its health right now, but will try to do that next week.

how do you 'test health' ?

with a battery tester, or failed OTAs, or ???

 

[dtbaker61]

I just had mine replaced last month, at 56,000 miles and 38 months of ownership.

No warning either, just turned off my car one evening, and would not start the next morning.

huh... well that's definitive!
did you ever, or periodically charge LVB to 100% ?
do any battery testing with a meter at dealership ?
get any warnings from failed OTAs ?

 

[dtbaker61]

My dealer service department replaced my AGM battery at around 35 months (barely within warranty) because they tested it and confirmed that it was failing.

with a meter, or with FDRS ?

But anyway, I suspected a dying LVB based on repeatedly failing OTA updates and the fact that the percentage reported on ford.com was generally around 40-60% instead of generally being around 80-90%, as measured by checking it daily for several weeks.

hhhmmmm thats a pretty good indicator. Did you ever leave your MME 'on' for a day or two to get the LVB up to 100% ?

 

[macchiaz-o]

with a meter, or with FDRS ?

I have no idea how the dealer tested. As I said, the service advisor said they cleaned up battery acid and he also mentioned that multiple 'cells' within the battery were toast. But I seriously doubt he accurately relayed to me what had been conveyed to him from the technician who did the real work. It didn't matter to me anyway... Battery replaced -- problem solved.

hhhmmmm thats a pretty good indicator. Did you ever leave your MME 'on' for a day or two to get the LVB up to 100% ?

I bought a Clore PL2320 and let that run overnight on several occasions. It'd allowed me to get certain OTA updates successfully installed, but after disconnecting it, when I'd monitor on ford.com, I could see that the higher charge level was quickly lost (within a day or two or whatever). So the homeostasis of the battery, if there is such a thing, was to remain at a significantly lower voltage than when it was brand new.

 

[dtbaker61]

I have no idea how the dealer tested. As I said, the service advisor said they cleaned up battery acid and he also mentioned that multiple 'cells' within the battery were toast. But I seriously doubt he accurately relayed to me what had been conveyed to him from the technician who did the real work. It didn't matter to me anyway... Battery replaced -- problem solved.



I bought a Clore PL2320 and let that run overnight on several occasions. It'd allowed me to get certain OTA updates successfully installed, but after disconnecting it, when I'd monitor on ford.com, I could see that the higher charge level was quickly lost (within a day or two or whatever). So the homeostasis of the battery, if there is such a thing, was to remain at a significantly lower voltage than when it was brand new.

It is not expected that the battery will stay anywhere near 100% charge because it is so small even the 2-hour shutdown process after you turn the car off will reduce the state of charge by 10%. The purpose of the 100% charge occasionally is to desulfate and retain as much capacity as possible for as long as possible.

Basically, holding the battery at a high voltage for a little while drives the deposited sulfate back into the electrolyte which makes more anode and cathode surface area available which retains energy capacity.

 

[macchiaz-o]

It is not expected that the battery will stay anywhere near 100% charge because it is so small even the 2-hour shutdown process after you turn the car off will reduce the state of charge by 10%. The purpose of the 100% charge occasionally is to desulfate and retain as much capacity as possible for as long as possible.

Basically, holding the battery at a high voltage for a little while drives the deposited sulfate back into the electrolyte which makes more anode and cathode surface area available which retains energy capacity.

To clarify, I meant that instead of staying at 85-90% (on ford.com) after an assist from the external power supply, I would observe it settle back down to 40-65%, which may have been an indication of less than stellar battery health.

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