12V Battery FAQ

[RedAero42]

I also extend thanks to Mach-Lee, super easy instructions. Our battery died last night at 44 months (100% of life in Phoenix and a single family home w/attached garage so the car is constantly "waking up"). It was a piece of cake! I went with the strut bar option.

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[AZBill]

I also extend thanks to Mach-Lee, super easy instructions. Our battery died last night at 44 months (100% of life in Phoenix and a single family home w/attached garage so the car is constantly "waking up"). It was a piece of cake! I went with the strut bar option.

I am also in Phoenix and ours lasted 50 months. I got a replacement H3-AGM at AutoZone and installed it today. When I reset the BMS, the alert in Ford Pass went away immediately, some people have reported several days to have that message go away.

 

[RedAero42]

I am also in Phoenix and ours lasted 50 months. I got a replacement H3-AGM at AutoZone and installed it today. When I reset the BMS, the alert in Ford Pass went away immediately, some people have reported several days to have that message go away.

Good stuff. I just went with the Ford dealer battery. 3 year warranty... almost good enough . And for the record our Ford Pass alert disappeared 2 days later.

 

[AZBill]

Good stuff. I just went with the Ford dealer battery. 3 year warranty... almost good enough . And for the record our Ford Pass alert disappeared 2 days later.

The AutoZone warranty is 4 years.

 

[Teslaeata]

Stangy’s at 50 months and your 12V time bomb still ticks

 

[Space_Pony]

The AutoZone warranty is 4 years.

Maybe that's why it costs 2 1/2 times more than the Motorcraft battery.

 

[jrt1701]

Do yall know why my EVSE clicks on as soon as i plug in once I get home? Is it topping off the 12v battery? It’s not really charging because it says in the app <1kw is going in and I have my car set to charge during off peak hours.

I do notice on the voltage read out on my uniden r7 it’s still hovering around 12.9-13.1v as if the car is still on too.

 

[CoyoteMach]

Mine clicks on as soon as it is plugged in, but in less than 30 seconds it clicks back off. It will then turn back on at the scheduled time (11pm).

I assume it is doing a test or validation event of some sort, and then it shuts off when satisfied.

 

[jrt1701]

Mine clicks on as soon as it is plugged in, but in less than 30 seconds it clicks back off. It will then turn back on at the scheduled time (11pm).

I assume it is doing a test or validation event of some sort, and then it shuts off when satisfied.

Mine stays "on" for more than 30 seconds it seems, but it does eventually switch off shortly before the car goes to sleep

 

[Teslaeata]

Do yall know why my EVSE clicks on as soon as i plug in once I get home? Is it topping off the 12v battery? It’s not really charging because it says in the app <1kw is going in and I have my car set to charge during off peak hours.

I do notice on the voltage read out on my uniden r7 it’s still hovering around 12.9-13.1v as if the car is still on too.

Unlikely that the wall box is charging your 12V batt because the BMS charges it from HVB via DC/DC converter when the car requires it, not when you connect the wall box.

 

[jrt1701]

Unlikely that the wall box is charging your 12V batt because the BMS charges it from HVB via DC/DC converter when the car requires it, not when you connect the wall box.

yes I’m aware the evse is not directly not charging it. On the first page of the faqs here it’s mentioned that one of the conditions the 12v is charged is when the car is actively charging the HV battery. So I was wondering if it’s pulling wall power to slightly charge the HV battery and then keeping the dc/dc converter active to top off the 12v for a little bit. I’ve also noticed the length of time it does this isn’t consistent either. Sometimes it’s longer than a minute sometimes shorter.

 

[Teslaeata]

yes I’m aware the evse is not directly not charging it. On the first page of the faqs here it’s mentioned that one of the conditions the 12v is charged is when the car is actively charging the HV battery. So I was wondering if it’s pulling wall power to slightly charge the HV battery and then keeping the dc/dc converter active to top off the 12v for a little bit. I’ve also noticed the length of time it does this isn’t consistent either. Sometimes it’s longer than a minute sometimes shorter.

I wouldn’t believe everything you read, even here

12V batt charging is virtually entirely unconnected with wall box charging.

Only remote link would be if HVB SoC drops under quite a low %age, can’t remember what it was and it changed at some point, such that HVB couldn’t charge LVB and then only when car was put on charge at wall box would 12V batt begin charging and even then only by HVB power through the DC/DC converter if 12V batt charging was required by BMS.

 

[JDS]

Need to be straightened out on when 12V charges


We did the latest update (25S65) in the driveway and the final step was a battery test, which resulted in a “charge and retest” result, as the cranking health wouldn’t show a result. The tech said I should take the car (10 month old 2024) into the dealer for a better test. The result at the dealer was that the car was 80% charged, and no codes concerning the battery were saved. However the battery failed the cranking test and was replaced on warranty.

I’ve tried to figure out how to keep the 12V charged on this forum using Mach Lee’s advice. The one piece of advice I relied upon was in the June 28, 2024 post it was: “The battery will auto recharge if it gets low,” I find that with the updates to the software making so many answers to the questions obsolete, it seems unclear how to keep it charged (other than using a maintenance charger). I thought that the updates would have the traction battery charge the 12V whenever it was low, whether or not the traction battery was charging or the car was on.

The dealer service guy said that the only time it charges is when we drive the car. This was just after the software update (25S65) that continues to charge the care for 12 minutes after the car is turned off. So I don’t think that he is as knowledgable as I would hope.

Long story short, with all the updates, when does the 12V charge?

 

[Mach-Lee]

Long story short, with all the updates, when does the 12V charge?

• When the car is ON (green READY light on dash)
  • And up to 12 minutes after being turned off with 25S65 update applied
• When you are charging the high voltage battery
• When the 12V battery gets below 55% SoC
  • Requires latest software updates (BCM+PCM) and the HVB to be above 20% SoC

 

[JDS]

• When the car is ON (green READY light on dash)
  • And up to 12 minutes after being turned off with 25S65 update applied
• When you are charging the high voltage battery
• When the 12V battery gets below 55% SoC
  • Requires latest software updates (BCM+PCM) and the HVB to be above 20% SoC

Thanks for answer! Sorry about repetition of prior questions.

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