[instantkevin]

you don't need a better battery... you need a better alternator...

I have 2 amps and a 1-farad capacitor. biggest improvement was made from new alternator (after the old one was overloaded and fell apart, literally). factory alternator pushes 60-75amps. I put in 100amp alternator... wonderfull! bass hit harder, no dimming headlights, no dead battery, nothing. it even charged my capacitor.
now i have a 150amp alternator. i think i can power a small house now.

sidenote: also... if you want good sound in your house too, buy a Onkyo or Harman Kardon stereo/surround reciever because they are both high current recievers (except the <$250 ones). this has the same effect in your home as it does in your car. these recievers deliver better sound at lower wattage ratings compared to most others. Too high of voltage, in car (i.e more than 14volts) or too high wattage in (stereo reciever) can cause excessive heat and damage to other components (i.e blown speakers, failed automotive electrical circuits). In case you're wondering... I sell electronics.

Get alternator, keep battery.