NO. Two tihngs:

1) No, you are not going to find a higher capacity battery - not such that it compensates for a problem like that.
2) Always remember, lead-acid type storage batteries are designed to provide 300 or more amps for a few seconds to start the car. THey are NOT happy when partly, slowly, discharged often - that will age the battery in no time.

2A) You don't need a bigger battery for "subs", the alternator is a 120 amp output version - at idle it can provide almost 1/2 it's output and at 1500 engine rpm, it can produce all 120 amps. Again, if you are going to sit with the engine shut off and audio system on, just know that it shortens battery life (unless you run a marine battery - which can provide 300 amps AND can tolerate partial discharge).


To find where your current is going, get an ammeter (or DVM), open the ground cable connection, and put the meter in series. Start pulling fuses until you find where it's going. That is the ONLY way to find it without spending tons of time.