what capacitor to buy?

donkason, a second battery isnt really necessary for too many installs...if you were having a power problem with 2 600W Kenwood amps off of a 180A alternator, I would first suspect that the 180A alternator isnt really 180A...either that or there were some other electrical demons involved...but there is no possible way that any 600W Kenwood amp is going to be close to drawing enough potential energy from your alternator to make your lights dim... if your lights are dimming, there are other possibilities that should be addressed...on alot of cars (especially Hondas) the stock grounding for the head lights is not sufficient, so it is always a good idea to replace the grounds for the headlights with heavier wire...that can solve alot of dimming headlight problems in itself...