[darkpuppet]

sorry should have explained a bit more.

All you want to do is install the second battery in parallel (fused of course) and with a diode isolator (you could get a solenoid isolator, but I prefer solid state) to ensure that the the 2nd battery won't drain the 1st if it dies, yet allow the alternator to charge it up.

You can find a lot of isolators from your local marine shops. Just make sure they're rated at the amperage your alternator is running at. Most of them operate up to 48 volts so I don't think voltage will be a problem.

what they tend to look like...


Also, a second battery setup is usually for listening to the stereo while the car is off... if you're doing it because your main battery is dying while listening to music with the car running, you'll probably want to upgrade your alternator to handle the load instead. If you're killing off 1 battery with your current stereo, a second battery doesn't solve matters.. you're still putting an exceptional load on the alternator which will eventually kill it.