How-To: remove and replace your 12v battery - recommended at 36 months

[dtbaker61]

It seems that you have the service manual for the job. I wonder what tightening torque is to

It seems that you have the service manual for the job. I wonder what the tightening torque for the black crossbar mounting nuts is. Does the the manual specify it?

I can't remember, but nuts that big I usually crank down "tight".

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[dtbaker61]

I wonder if / when a failing 12v battery could be detected by the BMS and warn me through the phone app before it is too weak to start the car.

The consequences of failure can be pretty high considering there is no warning.

? the 12v is not used to 'start the car' ?!

 

[Blue highway]

? the 12v is not used to 'start the car' ?!

it does "start" the car... if the 12v is too low, you can not "start" it. Once the module come to life, the dc to dc converter will carry it, but there has to be enough capacity left in the 12v get this to happen.

 

[dtbaker61]

Could someone explain how the 12v battery fails on an EV? In an ICE, my experience has been that the 12v just gets worse and worse at holding a charge until you reach the point where even after a few days, you are having to jump start the vehicle.

But on an EV like the MME, if that were happening, shouldn't the 12v just constantly be pinging the high voltage battery for more charge due to inability to hold a charge? How are these batteries having total failures without there first being a period of phantom drain or some notification that the 12v can't reach a charge above say 80%, 60%, 40%, 20%.

It is really hard to tell how bad the 12v battery is in an EV... since it is not turning over a starter/motor, it is difficult to notice as it gets 'weak'. I was watching voltage as it discharged/charged daily but that doesn't measure capacity.

As little as a week ago, the old battery was reaching 100% voltage, so that is not an indicator.

I recently bought a cheap $30 battery tester, which measures CCA and resistance... and that looked 'pretty good' last week at last measurement ... however, the failure was sudden, and the post-removal measure shows CCA well below 380, and the internal resistance way high. But, it was sudden, which is why I wrote this thread to warn people to be prepared.

 

[dtbaker61]

it does "start" the car... if the 12v is too low, you can not "start" it. Once the module come to life, the dc to dc converter will carry it, but there has to be enough capacity left in the 12v get this to happen.

well, ok, in that sense... 12v keeps the computer running, runs BT/modem that runs the locks, and once the capacity drops too low, the voltage sags under load (the monitor and all that consume about 250 watts when the car is on!), the computers error out, and the dc-dc never wakes up.

 

[21st Century Pony]

See FAQ "Can I replace the AGM battery with a lithium or LFP battery?"

Mach-Lee, this is a good primer. I remember reading it back in 202(3??)... nice of you to have reposted it here.

 

[360alaska]

I did this a few days ago, looking at it, I wonder if taking off the strut brace would be a better option than removing the frunk? I did it the normal way because I wasn't sure of the torque spec.

 

[Snakebitten]

In my opinion, I think the best way to not have a 12V failure sneak up on you is to find a method to monitor the AGM voltage when the vehicle has sat for a few hours.

Or put another way, if the AGM is holding a decent static voltage in the wee hours of the night, it's going to be there for you when you wake the car up to go somewhere.

The most typical Injured/tired battery is discernable after it has settled in for a few hours since it's last propping-up by an alternator/DC-DC Converter.

I use a cheap Bluetooth voltmeter that tattles on the static sitting battery without waking up the car/truck.

 

[Mach-Lee]

I wonder if / when a failing 12v battery could be detected by the BMS and warn me through the phone app before it is too weak to start the car.

The consequences of failure can be pretty high considering there is no warning.

Yes this is possible, Ford doesn’t do anything with that yet.

 

[Options]

Great advise my battery will be 12 months old in September I’ll make an appointment and let them do the work

 

[Space_Pony]

Great advise my battery will be 12 months old in September I’ll make an appointment and let them do the work

Are you going to replace a 12 month old battery? If so that seems to be a huge waste of resources. Do you replace your tires at 5,000 miles?

 

[Options]

Sorry my battery will be 36 months old in September

 

[dtbaker61]

Mach-Lee, this is a good primer. I remember reading it back in 202(3??)... nice of you to have reposted it here.

Mach-lee is the MAN on modern battery stuff! I am just a DIY solar/EV guy with 'transitional experience' having converted a couple gasoline vehicles to electric the hard way first with lead-acid, then lived thru the genesis of Lithium batteries (pre-BMS!) days running DC motors/controllers rather than AC .

 

[dtbaker61]

Sorry my battery will be 36 months old in September

its not a problem, just make sure your dealer has a new one on the shelf for you. Go in August and insist on a battery test, and try to get it replaced for free under warranty!

 

[Schmedlack]

so..... It might be just possible to get the old battery out WITHOUT pulling the tub.... but definitely would be tight fit. If I had to do it again, I'd try it this way.

I would note that the replacement battery in the video is a different size, without same foot-clamp to secure in place, and different ah, which would throw off the firmware parameters for capacity and charging. I would recommend sticking with 12v-35ah AGM H3 size... which you may have to ask Dealership to order.

I wanted to pull the tub to check out a few other things regardless.

Specifically, I wanted to add beefy cables to 12v connection points for charging/export of 12v. But that' a separate project...

Your words " without same foot-clamp to secure in place" is a big red light to me. I then reviewed the remove/replace video to see that the Walmart battery is not solidly mounted and can "flop around" in the vehicle. What if the car is in an accident? This is unsafe to me. What do you think? I know one thing, I would not drive around with a loose battery in any car, especially not my MachE.

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