Battery/Alternator Or What?

[Stay Alert]

I have a 2500watt system in my car and i have a cheap little wal-mart battery running it because my optima blue top battery died because the alternator failed. The alternator has been replaced but i am still on the wal-mart battery. The problem is when i am riding around playing the music the digital reading on my cap. falls below 10volts and then my
(4)subs starts sound crappy because of the voltage drop......but before i start the car the voltage reading on the cap is at 13volts but when i test the battery by itself its at 11.6.....i don't under stand what is going on could it be the battery or the alternator or something else please help.

[95mitsu03]

your system is draining too much power from the battery. plus the mitsubishis' shitty alternator is too slow to recharge the battery. I have the same issues and the only things I have on my car is a cheap cd player and aftermarket fog lamps. :x

[redboy]

ya ure either gonna have to make your car have two batteries, or get the biggest altenator, like the 130a or 140a big boy i think they sell for us, i think the stok one is like a 85 or 90 amp altenator. aint that hard, just a little thinkin on which way to go and how to du it......oh how many caps du u have, i hope not just one.......