Unless you want to listen to music with your engine off, adding a dedicated car audio battery won’t do you any good—and may even hurt you. That may seem counterintuitive, but the reasoning is simple.
How to Install a Second Car Stereo Battery in Your Vehicle!
The battery in your car serves one purpose: to provide enough amperage to start the engine. After the engine is running and the alternator is spinning, the battery acts as a load. If you add a second battery, it will act as a second load when the engine is running, because the alternator is keeping both batteries charged.
One battery is good, so two must be better, right? There are a few situations where that’s true. When the engine is not running, any accessories you turn on are drawing power directly from the battery. That’s why you’ll end up with a dead battery again if you accidentally leave your headlights on overnight. If you add a larger battery or a second battery, you’ll end up with some extra reserve power.
The main reason to add a second battery to a car or truck is if you need to use your accessories when the engine is not running. If you take your vehicle camping, that is a good example. You might be gone for a weekend or longer without running the engine, and that can quickly drain the battery. Adding a second battery allows you to drive longer without having to run the engine and recharge it.
