hmm.. ive run all kinds of amps for my subs.. with no caps on any of them. im sure that some needed some, but i was cheap and was saving for other things. id say, it depends on the amps, some draw a lot of current from the battery, and a cap is necessary. otherwise, unless you are pushing a true 500watts or more.. i would say you wouldnt need one. 1 farad for evey 1000watts. that seems to be the way to go.