1. What does the 12v battery do?
It is a lead acid battery that provides primary power for low voltage systems used to wake the car, Bluetooth receiver, lights, Sentry Mode, door locks, windows, latches, actuators, etc. When car is awake and high voltage (HV) contactors are closed, 12v support is supplied by the HV battery pack.
Life expectancy of a 12v battery can vary greatly from 2 to 4 or more years. Typically, they last about 3 years. There is no way to check the health of your 12v on your own. Of note, it is not recommended to hook up a 12v battery tender as this can adversely affect the vehicle’s management of the 12v system and lead to premature battery degradation and need for replacement.
Heavy use of accessories and things like Sentry Mode, that function while the HV contactors are open, put a strain on the 12v battery and can decrease its life expectancy. Extreme heat and bitter cold also may have an impact on the 12v battery’s longevity.
You may get a notification about needing to replace your 12v; it may also die without any advanced warning. Emission of a rotten egg smell is another indication of need for 12v service. If you get a notification don’t ignore it; make an appointment as soon as possible to swap out the 12v battery.
Although in some vehicles the battery may last up to 3 weeks after a notification, in others it may die soon after which may leave you inconveniently stranded. You can also go to a service center directly as many will take care of you as a “walk-in” for this type of urgent issue.
Without 12v support the car will be unresponsive and you will not be able to unlock the car, open doors, or charge. If you want to jump start the 12v, you need to manually open the frunk (method varies by model). Consult online user manual or Tesla Do It Yourself Support for instructions.
Make an appointment with Tesla service on your phone app. If your car has died, call Roadside Assistance, as your car may need to be towed to a service center if mobile service is unavailable.
Yes, you can purchase a 12v battery from Tesla “over the counter” and install it yourself if you are comfortable doing so. In order to be done correctly, the vehicle needs to be shut down completely, which involves disconnecting the HV battery. DIY is not recommended for Models S and X, particularly early versions, because the 12v in these vehicles is hard to access even for experienced techs.
Aftermarket batteries can be used, but at your own risk. Whereas early Model S vehicles are very particular about the 12v, late Model S and other models are more forgiving. Some owners have been happy with lithium-ion replacements which are longer lasting; however, caution is advised as the Tesla firmware in these vehicles was not designed for Li-ion 12v batteries.
That is up to you. If you are about to embark on a long trip and your 12v battery is over 3 years old, it may be worth the small cost to avoid the potential hassles of a dead 12v on a road trip.
10. Can running the high voltage battery pack to a low state of charge (SOC) affect the 12v? Yes, if the HV battery goes to very low SOC it may not support the 12v, so the car may “die” and not be able to charge without first jump starting the 12v battery even if you reach a charger in time.
It is warrantied for 4 yr or 50,000 mi, unless it dies because of something you did to it, like letting it go to a very low SOC. You can’t hide it from Tesla; logs will show what really happened before it died,
Instead of a lead acid 12v, the new Palladium Tesla vehicles have a 15-volt Li-ion battery that is used for low voltage system support. This battery is long lasting and not meant to need replacement.