Don't wait to replace the 12v battery at 3 years - just do it

[N1naz]

Every time we plug in the car and leave it plugged in (IE at Home) that 12v battery should be placed on/in a float state to maintain it, after an initial Bulk and Absorption stage. This is the way any other AGM Lead acid battery is/are maintained, if done right. I really do not think Ford does any kind of bulk/absorption/float on the batteries while plugged in. They just turn on the 12v charger and when the HVB charges to the set point percentage set by us the charging stops. Very bad practice. Yes, I know if it gets down to 40% it will turn on and charge the 12v battery, but does it do a Bulk/Absorption/Float type charge? I doubt it.
Mach-Lee of other users here might know more.

George M.

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[Mach-Lee]

Every time we plug in the car and leave it plugged in (IE at Home) that 12v battery should be placed on/in a float state to maintain it, after an initial Bulk and Absorption stage. This is the way any other AGM Lead acid battery is/are maintained, if done right. I really do not think Ford does any kind of bulk/absorption/float on the batteries while plugged in. They just turn on the 12v charger and when the HVB charges to the set point percentage set by us the charging stops. Very bad practice. Yes, I know if it gets down to 40% it will turn on and charge the 12v battery, but does it do a Bulk/Absorption/Float type charge? I doubt it.
Mach-Lee of other users here might know more.

George M.

Yes the 12V charging strategy is based on essentially Bulk/Absorption/Float logic (voltage will lower in stages at the battery is charged and approaches full). It's a little bit different because the BMS knows the exact state of charge and how to control the charging to achieve a target 90-100% charge. The strategy also interacts with how the vehicle is being used, for example it will go into a float mode while driving if the SoC is high enough, or bump up the voltage if there is a lot of 12V load on the system. It's much more complicated than just on or off. It's just shy about recharging the 12V battery when the car is off unless you have the latest software.

 

[N1naz]

Yes the 12V charging strategy is based on essentially Bulk/Absorption/Float logic (voltage will lower in stages at the battery is charged and approaches full). It's a little bit different because the BMS knows the exact state of charge and how to control the charging to achieve a target 90-100% charge. The strategy also interacts with how the vehicle is being used, for example it will go into a float mode while driving if the SoC is high enough, or bump up the voltage if there is a lot of 12V load on the system. It's much more complicated than just on or off. It's just shy about recharging the 12V battery when the car is off unless you have the latest software.

Thanks Lee, You mentioned the "lates software" do you have the software alphanumerics so I can check to see if my Mach-E has it please.

 

[AZBill]

For consideration:
There is no invisible barrier that definitely compels a 12v battery to be retired at 3 years. My '21 Premium passed 4 yrs in July '25. I occasionally check it's health stats with Car Scanner, and can envision the IPC/Ford App warning of oncoming decay appearing someday when the time has come.

That said any 12v can suddenly give up the ghost anytime. Only difference with an ICE vehicle is that you MIGHT get a warning sign with a slow turnover at startup. Perhaps the IPC/Ford App warning could be its equivalent.

FYI, My wife's Ford PHEV Fusion Energi just recently needed it's 12v replaced after continuous service since fall of 2016! It woke up nearly dead one morning.

I have a 21 MME that I purchased in June of 21, got the warning in Ford Pass in Aug of 25 and replaced it. Lasted 50 months, which is pretty good in the Arizona heat. Before I replaced it, I checked the resting voltage and it was 12.3V, which is low for an AGM.

 

[racker]

How did you get this graph?

This, along with a lot of other data, is collected via a Home Assistant integration, found here. https://github.com/marq24/ha-fordpass

You will need
- a working install of Home Assistant (https://www.home-assistant.io/getting-started/)
- HACS (https://www.hacs.xyz/)
- The integration (https://github.com/marq24/ha-fordpass)

 

[louc757]

I went to drive my car yesterday and saw UPDATE FAILED message. It looked like it had failed previously as well. I hadn’t been driving the car recently due to a couple of snow storms and I was traveling. I drove it for an hour yesterday, and I checked the SOC when I got home, and it was only 67%. I connected the Battery Minder and let it charge for 24 hours, and it is only at 78%. I took delivery Dec 17th, 22, so the battery is right at 3 years old. I ordered a new battery from RockAuto for $85 plus core charge and shipping. Thanks to @Mach-Lee for all the info on how to charge and change the 12V.

 

[allenj444]

Time is a killer. Is 36 months overkill? Probably, but it’s a more conservative approach. Because ….

I will definitely replace mine in 3 years, maybe even sooner. My 2025 Premium sat on the lot for several months before I bought it

 

[Kamuelaflyer]

I will definitely replace mine in 3 years, maybe even sooner. My 2025 Premium sat on the lot for several months before I bought it

Do a battery reconditioning sometime if you have a 12V charger that supports such a thing.

 

[allenj444]

Would the repair mode on this device work? I'm not having any issues...yet.

https://www.amazon.com/NOCO-GEN5X2-Fully-Automatic-Temperature-Compensation/dp/B08G3STB1N/ref=sr_1_22_sspa?crid=1L59T44KEREDN&dib=eyJ2IjoiMSJ9.esANIUStGmPiUyvXeDjdacc4C8xN9VGgVI9AruU8Q6wA558sisr_HsIsNUaYyEX9oRy6nm2mAOwIFGp-SfEk5WP2mOe4SXMFlUbaC7kj99r4AQ6LLe9U5FG6GoxL5b4zGPcFcNfyOmS86r0G85Cla5WojeAdBCyMBiFVzvohZKVWp6q5a8OUVTEZo9MXRCehnjs5BmhXdBvg515skmfTccXWBiHdV3_uLUIyiecZUe-GtMj9c7UqiTOcpWES0h5hFhSUwFIfNMfXus4JFxSx4-nzisgnqkn2n4bjnZbBFhk.-z47-RCh73WYUulVD_RfTg1qdXl16EGCSJp_g0T8AIk&dib_tag=se&keywords=noco+charger&qid=1766173185&sprefix=noco+charger,aps,138&sr=8-22-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9tdGY&th=1

 

[PebbleMav]

I went to drive my car yesterday and saw UPDATE FAILED message. It looked like it had failed previously as well. I hadn’t been driving the car recently due to a couple of snow storms and I was traveling. I drove it for an hour yesterday, and I checked the SOC when I got home, and it was only 67%. I connected the Battery Minder and let it charge for 24 hours, and it is only at 78%. I took delivery Dec 17th, 22, so the battery is right at 3 years old. I ordered a new battery from RockAuto for $85 plus core charge and shipping. Thanks to @Mach-Lee for all the info on how to charge and change the 12V.

 

[PebbleMav]

Also just ordered one at RockAuto.
Easily the best deal including shipping that I could find.

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