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When Did You Need to Replace Your 12V Battery?
- Thread starter PianoAl
- Start date
Black306
Active Member
IMO, short answer is no. Assuming there is nothing wrong with the car's 12v charging system (ie DC-to-DC converter and other related components), a voltmeter can be an accurate indicator of a bad battery if battery voltage is low. However, a normal voltage reading doesn't automatically mean the battery is good; a battery can still fail to deliver the amps needed to perform certain functions.
(Take the following with a grain of salt) Normally, I'd recommend people take their car to a local auto parts store and load test the battery. With Teslas, I probably wouldn't recommend it. With an ICE vehicle, 12v batteries aren't charged when the engine is off. I suspect when a Tesla is under a 12v load test, the 12v charing system will probably kick in to compensate. This may (a) alter the results by giving a false pass and/or (b) potentially damage the 12v charging system. I'd probably remove the battery and walk it into a parts store to have it tested. Hopefully someone with experience can chime in; I'd be curious if a 12v battery can be load tested while still in the car.
Jeremy3292
Active Member
I leave sentry mode on at work every day so I assume I am cycling my 12v heavily and it will wear out sooner than most.
Sentry Mode doesn't cycle the 12V battery at all. It puts extra stress on the high voltage battery and keeps the car awake the whole time, and the 12V battery actually stays fully charged.
Jeremy3292
Active Member
My understanding is when the 12v battery voltage gets low due to use (aka sentry mode), the HV battery connectors open and it then charges the 12v battery. That means the 12v battery is constantly being cycled with sentry mode on. I don't think the HV battery constantly keeps the 12v battery charged.
Well no, that's how it works when the car is sleeping. When Sentry Mode is on, the car never sleeps, and always runs off of the HV battery. And when the car is running off of the HV battery, it is charging/topping off the 12V battery. The 12V battery could not run Sentry Mode (which uses hundreds of watts) for very long.
smatthew
Active Member
Sentry mode uses like 250 watts. The car won't go to sleep until the idle load is under 5 watts or something small like that.
Last edited:
Jeremy3292
Active Member
Its extremely unlikely to be related to the 12V battery beginning to fail.
You could get a Tesla battery installed via the support center, or get a 'group 51R' battery and install it yourself. There are several threads about various makers of lithium based 51R batteries here on TMC, but the OEM battery back then was a 51R lead-acid battery made by Atlas (85B24LS is the model number I've seen at least once)
Just got my warning at 3.5 years and 68k miles. Normal 12v battery lifespan.
My question is where is the best place to buy one? Just looking for a standard replacement not an upgrade. I'd like to avoid tesla service since I'm outside of my bumper to bumper warranty. Batteries plus said they had nothing.
My question is where is the best place to buy one? Just looking for a standard replacement not an upgrade. I'd like to avoid tesla service since I'm outside of my bumper to bumper warranty. Batteries plus said they had nothing.
Black306
Active Member
Haven't replaced mine yet. From what I've seen others post, a battery from Tesla is significantly cheaper than any 3rd party. Might be worth putting in an order to at least inquire the price.
android04
Active Member
The battery costs $85 from Tesla, and you will not find an equivalent group size 51R battery for that cheap anywhere else. By the way, Batteries Plus does have group size 51R batteries that will work, but their battery match software (and that of all other auto parts stores) doesn't have any info for Teslas.
RayK
Active Member
As long as you are in an area serviced by a ranger (Tesla Mobile Service), I'd go that route. My pro-active replacement of the 12V battery back in June, just one month shy of 4 years old and at 23.5K miles, cost $119 including labor to install. Or as others have said, find a Group 51R battery and replace it yourself. Note that there's a HV disconnect procedure you must follow when replacing the 12V battery. I believe that this YouTube video covers the steps:
Ended up driving 1.5 hours to buy one directly from tesla. Didn't have the patience to deal with their BS service app or time to wait until next week for an on-site service call. It was indeed $85 plus tax. I read that on the forums here and there, but figured it was a pre-inflation, pre-supply chain catastrophe price.
I called the service center and the telsa phone robot told me to use the app to schedule service, got a person on the phone, he told me to use the app to schedule service. Even as I was there, in person, ,telling them "just give me a goddamn battery" they were like, did you schedule through the app? Why don't you get on the app? "I KNOW YOU HAVE TWENTY OF THESE IN THE BACK, JUST GIVE ME THE GODDAMN BATTERY."
Mission accomplished.
Install took all of ten minutes.
I called the service center and the telsa phone robot told me to use the app to schedule service, got a person on the phone, he told me to use the app to schedule service. Even as I was there, in person, ,telling them "just give me a goddamn battery" they were like, did you schedule through the app? Why don't you get on the app? "I KNOW YOU HAVE TWENTY OF THESE IN THE BACK, JUST GIVE ME THE GODDAMN BATTERY."
Mission accomplished.
Install took all of ten minutes.
Black306
Active Member
1,356 days (3 years, 8 months, 16 days) and 8,936 miles later, warnings popped up after pulling into the garage; 'Low Voltage Battery' and 'Electrical System Power Reduced/Vehicle Shutting Down.'
Took delivery of my 2018 Model 3 LR w/ Performance Boost in November 2019. Just hit 86,000 miles and got the dreaded 12v warning. Submitted a service request Saturday and got an appointment for today. The technician just left, and the cost was $117.42. I'm pleased. I may possibly have done it myself for slightly cheaper but with WAY more hassle.
Kimmi
Member
Mine was replaced under warranty at 3 1/2 years with 27K miles. Got the warning and the battery was dead one hour later. 
davewill
Active Member
My 2019 M3 complained about the battery a few months before my warranty was to run out. Tesla came out and replaced it free of charge.
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