“The electric vehicle revolution is here, and it’s going to solve all the issues that plague gas cars.” – Nobody

Many enthusiastic EV owners and owners-to-be love to extol the virtues of low maintenance and high reliability on their cars. And that’s for good reason: EVs have a fraction of the moving parts of a gas car, with far fewer failure points. However, EVs are not a panacea or a fix-all. There are still some maintenance items to be aware of on an EV, and today we’re covering the 12-volt battery. We also have more general information available on full EV maintenance. 

Why 12 volts?

Just like a gas car, an electric vehicle has a 12-volt battery to power accessories and security functions while the car is parked. This is true from Chevrolet to Tesla, from Hyundai to Rivian. 12-volt systems have remained popular due to their minimal wire gauge requirements and the fact that the same parts can be used for gas and electric cars. 

However, all 12V batteries are not created equal.

Earlier EV 12V batteries were generally the sealed lead acid (SLA) variant. These use the same chemistry as most modern gasoline cars. However, some EV owners report their 12V battery dying in just 2-3 years after obtaining their EV. We think this may be due to increased accessory use in EVs compared to gas cars. 

Here are a couple real-world quotes from people who have found their 12V battery drained in atypical circumstances:

“I am relatively new to Electric cars and have had my Kona for 2 months. Just got back last night from a 6 hour drive and I [think] we left the boot slightly open all night. Just now I have gone out to close the boot and the car is completely dead.” – Hyundai Kona Forum

In this case, the driver found a clear culprit: accessory lights from an open hatch drained the 12V battery overnight. 

Last night I parked my 18 month old 2017 Bolt EV with about 5400 miles in my garage. It showed 150 miles remaining range, and I didn't plug it in. This afternoon, I found that it wouldn't respond to the fob, wouldn't respond to door button presses, and when I plugged it in, the charge light didn't come on. Later, when I had time, I got in with the key. I checked the 12V battery voltage; it was 3.6. – MyChevyBolt.com forum 

One important thing this user highlights is the power lock system on the Bolt EV. It depends on having a functioning 12V system, and without it, you’re hard pressed to easily unlock your car.

“Recently got a 2022 Kona EV, today the it won’t start - no interior lights, BlueLink won’t connect, the works. I’m lost as to what to do.” – r/KonaEV

In cases like this one, having a PDF of your car’s manual saved on your phone – and your tow service’s number in your phonebook – are good contingency plans.

“It seems so silly that an electric car can be crippled by a 12v battery issue. I had never received any warnings about the battery so it all hit me at once. I feel a lot better now and mostly because of what the [tow truck] driver said, “everything breaks down”. At the end of the day it is still a car.” – r/TeslaMotors

Perhaps most poignant is this last observation: “At the end of the day it is still a car.” With respect to the accessory system, little will probably change in EVs until the entire industry has decided on a new standard for accessory power.

Unique solutions

In the Tesla Model 3/Y, there is a unique procedure for jumping or removing the 12V battery when it dies. This procedure may not be known to tow companies or individuals who need to access a dead battery. In brief, there is a port on the front of the car that can opened to reveal a wiring harness. Hook that up to a 9V battery (or a 12V battery source) and the frunk will pop open - if and only if the 12V battery is completely dead. Once open, you can then remove the access panel that normally covers the 12V battery. Consult your Tesla owner’s manual for more information. 

What else should you know about the Tesla 12V battery? As of 2022, Tesla is shipping cars with lithium 12V batteries which should last years longer than the SLA batteries previously equipped on Tesla cars. Other manufacturers are following suit, so be sure to check your vehicle’s specs so you are aware of the 12V battery replacement schedule. Then, set a calendar alert to preempt needing to replace one in an emergency.

Conclusion

Overall, unless your manufacturer has issued a recall about 12V batteries, you shouldn't have much to worry about for the first several years of ownership. That is, unless you leave a door open or accessories on overnight. The biggest takeaway is to know how to unlock and/or jump start your car if that battery does need servicing. Your vehicle’s user manual will be the place to check.