2017 BMW 740i Base Car and Truck Battery

What Is An Auxiliary Battery

What Is an Auxiliary Battery?

These batteries are designed to run as a backup to the starting battery and provide power to some essential equipment like engine start/stop and other systems that require power while the engine is off to put less strain on the main battery and alternator.

Where is the Auxiliary Battery?

If you can't find or no longer have your car's owner's manual to look up the location of the batteries, you could also get your hands a little dirty and look in the car. Auxiliary batteries are not always as easy to find as your main starting battery. It could certainly be under the hood but it could also be under a seat, behind the glovebox or somewhere in the trunk.