12 Volt battery warning.

12 Volt battery warning.

I finally got my model 3 back from the Tesla Certified auto body shop after getting rear ended in June. The body work is superb and my car looks like new. While the car was in the shop, they allowed my battery to go below 10 miles before they put it on the charge. We picked up our car yesterday and the 12 Volt Battery light was on. They called Tesla and they told them, when I drive the car, the light will go off, but it didn’t. Has anyone else had this issue? The auto body shop said they will give me a new battery if I need it. I’m not sure if it’s because the charge went down so low or if I actually do bed a new battery. My car was only 3 months old when I was hit.

gballant4570 | 27 augustus 2019

Not usual for a 3 month old car to lose the 12v battery. I do not know if letting your main battery go that low would have caused the 12v battery to go bad though....perhaps someone else will.

tdrager | 28 augustus 2019

If the sealed lead-acid (SLA) battery was allowed to run down, it was permanently damaged. Probably one of the six 2 Volt cells was reversed, and now you have a battery reading 11.6 Volts while charging instead of 13.6 Volts, hence the warning. Plus, the higher current being continuously pumped into that SLA battery could cause it to out-gas hydrogen and further degrade other cells.

Time for a new 12 Volt battery, for safety reasons.

AWDTesla | 28 augustus 2019

So cool our cars tell us this instead of some light and then plugging in a device to retrieve a code, then search on the internet for the codes meaning.

But yeah, you need a new battery. sounds like the body shop let your car run a while if it got the actual big battery down to 10.

Which leads me to my next question....

We get weak batteries here all the time because of our cold weather. sometimes a 4 or 5 year old battery will start to crank really slow and taking it out and checking/filling the cells with distilled water, throwing it on a charger for 24 hours will usually refresh it for another 4 or 5 years.

Can you put a tired 12 volt Tesla battery on a charger?

Ron.Olsberg | 28 augustus 2019

It is my understanding, if the car is not being driven traction battery should not go below 20% (which is way more than 10 miles range). When the car gets down to 20%, the 12V AGM battery will not be maintained. I am not sure if the car is smart enough to shut down all 12v power draw sources (I believe it is not). The best approach is to disconnect the negative 12V terminal if the car will set for more than a week or two. If you disconnect the 12V battery terminal, the car will not just go to sleep it will be in a comma. If the car is parked outside at very low/high temps approx -22F/110F and the 12V is disconnected, the traction battery could be damaged because the battery management system can not maintain safe battery temps. Please feel free to correct/clarify my comments in this post.

mmcp42 | 28 augustus 2019

I suspect OP meant 10 VOLTS not 10 MILES

tdrager | 28 augustus 2019

AGM lead batteries like to be at 100% ALL THE TIME to maximize longevity. Lead batteries are required in most old and new cars because:

- No intelligent BMS required. Always keep them topped at 13.3 to 13.6 Volts. Easy.
- Temperature tolerant, much more so than Lithium. No thermal management required.
Charge and discharge in any temperature.
- Cheap, well-understood technology

Our lithium traction battery won’t be hurt in discharge mode at any temperature. However, charging at low temperatures may cause lithium plating and capacity loss. See

jjgunn | 28 augustus 2019

Cool info @tdrager - Thx!!

Frank99 | 28 augustus 2019

>>> charging at low temperatures may cause lithium plating and capacity loss
Which is why Tesla heats the battery to safe levels before charging if it's too cold...

Janice.ribeiro | 28 augustus 2019

my husband stopped by Tesla today and they did tell him because the auto body shop ( Tesla certified) didn’t charge my car until my battery had 10 miles left to it, and it went in the red, my 12 volt battery was ruined. The auto body shop is replacing it for me.

Janice.ribeiro | 28 augustus 2019

@mmcp42, It was 10 miles left to the charge. I don’t know why they let it go down so low before they put my car on the charge.

shippersm | 8 december 2019

I have the alert 12 V battery; My model 3 is 5 days old !

Magic 8 Ball | 8 december 2019

@shippersm Congrats on your new Tesla. These thing are rare but they do happen. You got a short straw but they will take care of you. Nothing to be overly excited about.