An electrical storage device used to supply electrical current for starting a vehicle.Checked 2026-08-16
12-volt battery
The low-voltage battery that powers control systems and, on combustion cars, supplies starter current.
Also called: 12V battery · starter battery · auxiliary battery · low-voltage battery
What it means
Definition
On a combustion vehicle, the 12-volt battery stores electrical energy and supplies the high current needed for starting as well as low-voltage loads when the engine is off. Hybrids and EVs also use a low-voltage battery to wake computers, operate controls and close the high-voltage battery contactors even though it does not propel the car.
Why a buyer cares
What it changes
A hybrid or EV can have a healthy traction battery and still fail to become ready because its low-voltage battery is weak. The 12-volt battery and high-voltage traction battery are separate systems.
In practice
Where you meet it
Under the hood, in the trunk or under a seat, and on battery-test or replacement records.
Two things that look alike
Not the same as
The 12-volt battery powers low-voltage systems; the traction battery stores energy for electric propulsion.
Read next
Related terms
Starter motor and solenoid
The electric motor that cranks the engine and the switch that engages it with the flywheel.
Alternator and charging system
The belt-driven generator that keeps the battery charged and runs the car's electrics while the engine is running.
Hybrid traction battery
The high-voltage pack that drives a hybrid's electric motor, separate from the 12-volt battery that starts the car.
EV DC/DC converter and onboard charger
The onboard charger fills the high-voltage battery; the DC/DC converter supplies the car’s low-voltage system.
Where this comes from
Sources
DC/DC converter: This device converts higher-voltage DC power from the traction battery pack to the lower-voltage DC power needed to run vehicle accessories and recharge the auxiliary battery.Checked 2026-08-16
Nominal low-voltage architecture and battery chemistry vary; ‘12-volt’ remains the common service term.