make a cheap isolated dual-battery setup
Crutchfield's Amplifier Wiring Diagram -- Info you can use!
This boombox is made out of a car radio, salvaged speakers, and two lead acid batteries. Plays for 9 hours continuously! (Tech Gadgets Tips)
car audio simple set up
1/0 4 8 awg Gauge ga Nickel HEAVY DUTY BATTERY Terminal Positive in Consumer Electronics, Vehicle Electronics & GPS, Car Audio & Video Installation | eBay
Pair of ILL Customz (8) 1/0 AWG Wire Car Audio Battery Terminals BOLT DOWN | Consumer Electronics, Vehicle Electronics & GPS, Car Audio & Video Installation | eBay!