To gain 12 volts, that most car amplifiers need to operate, you need to connect the positive wire to the positive terminal on that car battery. This guide might be useful if you want to run a car amplifier in your home, with using a spare car battery. The only negative about wiring a car battery in your home is, it will drain fast because it does not have a alternator to charge it up.
Instructions on how to wire a car battery to a car amplifier:
1)Firstly, if you don't already have a car amp wiring kit, then go buy one. If you have it, then move onto step 2.
2)In your wiring kit it will contain, a ground wire (black colour) and a power wire (red colour).
3)Locate you amp and unscrew the terminals were its appropriate to insert the positive wire in, do the same for the grounding wire as well.
4)Now insert the both wires into the appropriate terminals correctly and then screw both terminals on the car amp.
5)Now locate your battery's positive post and connect the power wire onto it. Now you either have a choice of grounding your car amp, using the negative on the battery or using metal to act as a ground. If you choose to use your battery as a ground for your car amp, then connect the grounding wire from the amp to the negative post on the battery.