Do I Need an Extra Battery for Running My Car Audio Subwoofer?
You can install your car audio subwoofer to run using your car's existing electrical systems. No extra batteries are required to add a subwoofer to your car. You can make certain parts of the process easier, by using a 9-volt battery during the installation process, to figure out which wires are positive and negative. In order to do this, take a disconnected speaker and touch its wires to the battery. If the speaker moves out, the connections are positive to positive and negative to negative. If the speaker moves in, it is the reverse.
However, the 9-volt battery is not a part of the final installation.