Tesla Service UK / Guides / 12V / 16V battery
Tesla low-voltage battery warning: 12V or 16V, and what to do
Every Tesla has a small low-voltage battery as well as the big drive battery. If it fails, the car may not unlock, wake up or drive — even with a full main battery. Here's how to tell which type you have and what to do about a warning.
Last fact-checked: by the XKey Developments team. General guidance — always check your own car's details and current official sources. Repair costs vary by car and garage, so we don't quote prices: ask for a written quote.
Which battery?
12V lead-acid or 16V lithium?
As a general guide:1
- 12V lead-acid: Model S and Model X built before the 2021 refresh, and Model 3 and Model Y built before late 2021.
- Lithium-ion low-voltage battery (usually around 16V): the 2021-on Model S and Model X, Model 3 and Model Y from late 2021, and the refreshed Model 3 and Model Y.
The two types are not interchangeable. Check your own car's owner's manual, or ask the garage to confirm from the VIN, before buying anything.
Warnings
What the warning means
The car may show an alert such as "12V battery needs service" or a message that the car needs service and power may be reduced. On lithium cars the warning typically appears days to a couple of weeks before it fails; lead-acid batteries sometimes die with little or no warning.1
Don't ignore it. If the low-voltage battery fails, the car can't connect the main battery, so it won't drive, and it may not respond to the phone key or key card. Book it in before an important trip.
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If it's flat
If the car won't wake up
- Use your owner's manual's procedure for giving the car external 12V power to open the frunk and reach the battery. It is there to wake the car, not to fix a failing battery.
- Don't use a Tesla to jump-start another car, and don't improvise with another car's battery — use a portable jump pack only as the manual describes.
- If you're stuck, Tesla Roadside Assistance can help — see how to contact Tesla UK.
Replacement
Who can replace it?
Replacing a 12V lead-acid battery is a routine job that most independent EV specialists can do. Lithium low-voltage batteries are more often handled by Tesla or Tesla Mobile Service, though some independents now do them too — ask when you call. On a car still within its basic warranty, the battery is generally covered, so try Tesla first (see our warranty guide).
Early warning signs, such as a slow-to-wake car or a screen that keeps rebooting, are covered in our 12V warning signs guide.
Find a garage that can test and replace it near you
Independent EV specialists, mobile technicians and Tesla Service Centres near your postcode.
Search by postcode or townOr browse: HEVRA-accredited EV specialists · independent & mobile garages · Tesla Service Centres · by town or county