An automotive audio battery works in the same way as a traditional car battery, but it is dedicated to powering your vehicle’s audio needs. Factory-installed batteries can power basic audio functions, but a high-end audio system requires extra juice to work effectively. Amplifiers are especially power-reliant and will not work at their optimum level without an extra source of power. If the car is spreading around its power too thinly, this will negatively impact some of the other electrical features around the vehicle such as the windows and headlights.
A second battery allows you to double your stored power, so you can enjoy your audio system without negatively impacting the other features around your car. It gives you plenty of reserve amperage, particularly if you place the battery very close to the amplifier. Batteries come in a range of different sizes and power capacities, so you can choose the one which comfortably covers all the functions in your vehicle.
Generally, installing a second car battery should be a relatively straightforward procedure. The most common location is in the trunk as you are unlikely to be able to put it in the engine without making some pretty serious modifications. Otherwise, you could put it under the load tray or in the passenger compartment. Essentially, you want to keep it from getting too hot, which could prove to be a problem for the battery. Depending on how much space you have available in the car, you may have to choose a battery which is physically similar to the original one which you already have. Often, they are wired into the vehicle, so your second battery can continue charging while you are driving. A high-amperage on/off switch then allows you to switch to the second battery when you are parked to stop the main one from draining. However, you need to remember to flick that switch to ensure that the right battery is being used at the right time!