I find that alternator hard to belive at that price, its to cheap... but that is another issue.

i origonally asked for the model number and brand of the amps because if you really need some extra power then i was going to make the suggestion that was made above about the ABC's however being as you seem to think 150 for a high output alternator is to much im going to also assume you are running amps that didnt cost that when combined that being said you have no need upgrade the alternator battery or add caps.

A word of advice when people are trying to help you is to help yourself and awnser the questions they ask.