Bro, depende sa rating ng audio setup mo na ilalagay dyan... as for the HID, it really doesn't take much current, kasi 35W lang yan, kahit 55W na HID, di pa din mararamdaman ng stock alternator mo yan...

Kung JBL amps naman gamit mo, kung GTO series lang yan, they wont really eat up a lot of current... capacitor na lang ang idagdag mo. Or kung gusto mo din maka-sure pa, if you have currently, say, a 1SNF battery, go buy yourself a size bigger than it...