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

[allenj444]

Batteries that pass all tests can fail suddenly.

Very true

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[Mach-Lee]

I have a tangential question:

I have a '22 GT that I bought in July of this year. The car was put into service in May of 22 so it was already over 3 years old when I bought it. I didnt think too much of the 12v battery until I started having problems with a specific OTA update that kept complaining that the 12v battery was too low. Not long after, I picked up an OBDII scanner so I could see that the 12v battery was fluctuating between 65% and 85% (but usually below the 80% that was needed for this particular OTA).

Both me and my local dealer tested the battery and it "passed", though I did note that the voltage was about 12.5v after charging with my external charger to 100% instead of the more expected 12.85v. When I coupled the stuggle to get over 80%, the lower voltage, and the "3 year" warnings Ive seen here on the forum, I had it in the back of my mind that the battery was probably not long for this world.

Fast forward to last week: I went to turn the car on and the red battery MIL was on on the dash. So I figured "today's the day" and I replaced the battery without really diagnosing the problem (had the dealer do it, too busy atm to tackle myself).

Since its been replaced, Ive been noting some weird SOC reports from OBDII. When I got home from the 20 minute ride home from the dealer, the SOC was about 75%, which at the time I was a little surprised it wasnt closer to 90+ but I chaulked up to recent BMS reset, short drive, whatever. However, I have been noting that it seems to just be depleting without ever charging. It got down to about 50% before I decided to set my EVSE to 6A and let the car charge over night.

In the morning, after maybe 18 hours on the L2 at 6A, the 12v battery was still only in the mid 70s SOC, and it continues with the "I lose 5% ish each time I drive it" behavior. I'm now back down into the 60s/50s. I know the battery takes a hit each time we start the car and it struggles to charge if you only drive short trips, but it feels like its not really charging at all.

I do see the OBDII reports that the voltage is 14.5v while the car is on, which implies the DC/DC inverter is working (though I should confirm with a multi-meter on the battery terminals directly).

My question is this? Does this sound normal? Or does it sound like perhaps I am having a DC/DC inverter issue. The car has been driving fine, and no dash MILs are illuminated, so part of me is thinking that the car is just adjusting to the reset BMS and it will be fine eventually. I.e. the only reason I am suspicious is because I am watching the SOC. But the other part of me is wondering if I just let it go im going to find myself stranded with a dead 12v system.

Sounds like you might possibly have a battery drain, can you check this out for ideas? Troubleshooting "Electrical System Drain Service Required" Message

Also remember that if you leave an OBDII device plugged in and it's actively collecting data (like if you forgot to quit the app) the car will stay awake and drain the 12V battery. I would suggest unplugging the OBDII device when you park the car to rule that out.

Assuming you are getting 6+ hour charge periods in, the 12V should be somewhere in the 70-90% range typically.

Last, make sure you have the "Share vehicle data" setting turned on in vehicle privacy settings so you'll get the alerts in the Ford app about 12V battery or electrical drains.

 

[ChasingCoral]

Well, I learned a new lesson today that I feel foolish to have ignored. Just 2 months ago, I took my Mach-E to the dealer and had them 'check on' the 12v battery' (they said it was 'fine'). I also had any and all recalls/updates taken care of. This past weekend, my EV's 12v gave out. All of a sudden. No warnings leading up to it. It was in a colder place (25deg F ovenight), and it usually lives in temperate southern California near the coast in a garage. Just blitzed out when I got in it, displayed all the error warnings on the dash, flashed the hazard lights, protective door latch guarded from a lock-in, pulsed the brake pedal, etc. and then went into 'low battery' mode, then finally 'door would not even open' mode. Had to be dragged up onto and towed on a flat bed to the nearest dealer (which was far away from my location, so I had to pay a lot extra for the towing even though I have Ford Roadside Assistance). I will never make that mistake again. The car is 40 months old. I should have insisted that at 3 years, and no longer than 3 years, replace the 12-volt. battery. I recommend you do the same if you have the chance.

Agreed. something similar happened to my wife while I was away on a long kayak trip.

When preparing for a long trailer trip in the Lightning this summer right after the 3-years was up, I replaced the battery. I didn't want to find myself looking for the right battery in remote areas of Ontario.

 

[ghaskins]

Sounds like you might possibly have a battery drain, can you check this out for ideas? Troubleshooting "Electrical System Drain Service Required" Message

Also remember that if you leave an OBDII device plugged in and it's actively collecting data (like if you forgot to quit the app) the car will stay awake and drain the 12V battery. I would suggest unplugging the OBDII device when you park the car to rule that out.

Assuming you are getting 6+ hour charge periods in, the 12V should be somewhere in the 70-90% range typically.

Last, make sure you have the "Share vehicle data" setting turned on in vehicle privacy settings so you'll get the alerts in the Ford app about 12V battery or electrical drains.

Thanks for the info. I don’t see anything in the list that is obvious, and I don’t leave the OBD reader connected. I do have the Welcome Lighting turned off so I might try some experiments with that. I haven’t seen the Drain Warning yet, though, so I’ll keep an eye out for that.

 

[ghaskins]

Thanks for the info. I don’t see anything in the list that is obvious, and I don’t leave the OBD reader connected. I do have the Welcome Lighting turned off so I might try some experiments with that. I haven’t seen the Drain Warning yet, though, so I’ll keep an eye out for that.

Sorry, I meant I do currently have the welcome lighting ON.

 

[JmanMachE]

I replaced mine at Ford for about $300. I figured they’d do the labor and resets so why not. Testing AGM type battery for health is not reliable, they are prone to sudden failure. No reason to take that chance.

 

[ghaskins]

As an update, I just did the following:

Plugged in the OBDII and read 12v SOC as 53%. Popped the hood: Battery voltage was 12.61v and tester said 80%/Good. I charged it to 100%, noted the voltage was now 12.88v, and did the BMS reset. I drove it around town with the OBD connected, expecting to see the SOC value eventually recalibrate but all it did was continue to drop. It was at 50% when I got home.

Given the discrepancy between the OBD reading and the external facts (12.6v, 80% SOC, which both seem believable since it the battery is only a few days old), could I be having some kind of problem with the BMS sensor?

 

[JohnFoxeSheets]

As an update, I just did the following:

Plugged in the OBDII and read 12v SOC as 53%. Popped the hood: Battery voltage was 12.61v and tester said 80%/Good. I charged it to 100%, noted the voltage was now 12.88v, and did the BMS reset. I drove it around town with the OBD connected, expecting to see the SOC value eventually recalibrate but all it did was continue to drop. It was at 50% when I got home.

Given the discrepancy between the OBD reading and the external facts (12.6v, 80% SOC, which both seem believable since it the battery is only a few days old), could I be having some kind of problem with the BMS sensor?

Could be. I’d call the dealership that did the battery swap.

 

[Mach-Lee]

As an update, I just did the following:

Plugged in the OBDII and read 12v SOC as 53%. Popped the hood: Battery voltage was 12.61v and tester said 80%/Good. I charged it to 100%, noted the voltage was now 12.88v, and did the BMS reset. I drove it around town with the OBD connected, expecting to see the SOC value eventually recalibrate but all it did was continue to drop. It was at 50% when I got home.

Given the discrepancy between the OBD reading and the external facts (12.6v, 80% SOC, which both seem believable since it the battery is only a few days old), could I be having some kind of problem with the BMS sensor?

What was the battery voltage while you were driving around? It should be at 12.9V or more.

After you reset the BMS, the % SoC also needs to calibrate after you turn the car off for 6-8 hours in order to be accurate. If you reset the BMS and immediately go for a drive, it might do weird things (like assume 50% SoC as a failsafe) until it can sort things out.

 

[ghaskins]

What was the battery voltage while you were driving around? It should be at 12.9V or more.

The only PID I know shows the voltage at 14.50-15.10 while driving, which I attribute to the DC/DC inverter doing the 12v charging like an alternator in an ICE car. Not sure this is what I should be looking at.

After you reset the BMS, the % SoC also needs to calibrate after you turn the car off for 6-8 hours in order to be accurate. If you reset the BMS and immediately go for a drive, it might do weird things (like assume 50% SoC as a failsafe) until it can sort things out.

Ah, that makes sense...I'll check it out later this evening or tomorrow. Thank you for all of the tips.

 

[flapjake314]

is it absolutely necessary to charge the new 12V battery to full? are you all buying a 12V charger before you change the battery yourself?

 

[McSquashy]

My 2023 will be celebrating it's 3rd birthday in June. I've already been planning it's 12V battery transplant since shortly after taking delivery in March of last year.

 

[GreaseMonkey]

is it absolutely necessary to charge the new 12V battery to full? are you all buying a 12V charger before you change the battery yourself?

That would be the ideal scenario, yes. I charged a 2-year old MME battery using a good charger while it was installed on the vehicle and it took FOREVER to reach 100%. A test of my patience.

 

[Wenatchee Mach E]

I had a similar problem. Dealer checked the battery at the three year time and said it was fine. About three months later I got a check battery warning in Fordpass, so I got a new battery. The car is about 3 1/2 years old, and only 12600 miles, but all of my driving is short runs of 1 to 3 miles 4 to 5 times a day, and the 12 volt has to work every time you stop and start.

 

[ChrisO]

I had a similar problem. Dealer checked the battery at the three year time and said it was fine. About three months later I got a check battery warning in Fordpass, so I got a new battery. The car is about 3 1/2 years old, and only 12600 miles, but all of my driving is short runs of 1 to 3 miles 4 to 5 times a day, and the 12 volt has to work every time you stop and start.

In fact, the 12-volt battery powers almost everything other than the drive motors, DC/DC converter, and thermal management.

We are talking accessories, lights, control modules, displays, cabin fans, door locks, air bags, ...

It isn't just used to "start the car".

I was mistaken.

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