BMW 335i Auxiliary Battery Replacement at your home or office.

What is the Auxiliary Battery all about?

The vast majority of passenger vehicles on the road today have only a single, large battery. It’s generally located under the hood, although some makes and models have the primary battery in the trunk, near the spare tire. This battery’s job is simple – it provides the electricity needed to start the engine. All other power generated during operation to power the radio, signal lights, and other accessories comes from the alternator.

However, some vehicles (notably higher-end European imports) have more than one battery. There’s the primary battery under the hood, but there’s also an auxiliary battery. These are used to power other systems on the car that require 12 volts of power, and which the alternator is not capable of powering directly. In these instances, the alternator is responsible for charging both the primary and the auxiliary battery. The primary battery delivers voltage during cranking, and the auxiliary battery runs some or most of the car’s accessories.

Like all batteries, auxiliary batteries will eventually wear out or fail. When this happens, they’ll need to be replaced.