i've ran my SD8000.1 off a stock battery lol, and one run of 4/0 gauge to the back on music and been fine in spurts. 300amp alt though. lots of voltage drop, but the amp is fine down to 9v and produces power that low. if you play your music full tilt for minutes at a time then you probably need 2 or 3 batteries, if running tones 4 is probably fine.
everyone on here is going to disagree with me though most likely. lots of electrical overkill on this forum, which is a good thing lol, but you can skimp by with less. especially if not metering, the difference between 5k and 6k isn't too noticeable so just turn the gain down slightly