[Subix]

What kind of battery is it? cranking/cold cranking amps? Maybe you got a weak ass battery to begin with? (low crank amps whatnot, generic battery)

I'll have to agree that it sounds like a crap battery to me. I have a 450 watt sub in my trunk and will sit with key set to ACC and listen to music for about 40 minutes or so several times before waiting on something and never had an issue. Of course, I did worry that it could drain/kill my battery but it never did.

You may be right about the alternator though. If the thing is on its way out it could only be charging the battery minimal at best, never having a full charge to begin with... so you'd be running off half or low battery anyways.

I'd get them both tested.