i currently have an amp connected to my two front and two rear speakers. i am now thinking of buying a sub off a friend... which also has an amp....what would be the best thing to do. would i use two amps. or run the sub and the speakers of one amp....whats most effective and would using two amps kill my battery....also it is a (pioneer) 12" sub in box with amp mounted on box for$300 .is that a good price???

I wouldn't pay more than $200. But I'm a cheap bastard. Depends on what model/power/age/condition.

But, if the amp is matched to the sub and your happy with your current set up then I would just plug and play the sub. Running 2 amplifiers off of the battery will be fine, just don't be a dumbass and play your stereo loud in the carpark and you should be fine.

Kieran

Running two amps won't kill your battery
Is the amp with the sub a monoblock? Sub's run better off mono's
What are the model numbers?
What sized power wiring are you running to your amps?