battery FOR SURE....caps only really help if you have the extra juice to back them, and if you dont have a HO alternator, then the cap is pretttttty much a waste of money. get red top or yellow top (or a kenetik battery if you can get one at a good price) and upgrade your power wires, and the big 3 (SEARCH BIG 3). you WILL hear a differance between a nice battery with good power wire + big 3 from a stock battery with no big 3 upgrades. i have 2 red tops and a stock 90amp alty and i can manage to stay around 12v at a full 2500w full tilt, though when im idling i turn it down so my atlys sake...when i started off with car audio i tried several differant kinds of caps and almost every time it was a waste of money, and then when they get old and break (cant keep a charge) they tend to help drain power //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif