how do you install a secound battery just hook one more up tot he stock one, or do i need a nother alternator?

 

best way is to hook it in parallel (neg to neg pos to pos) with a fuse on both ends depending on how far it is away from the first (if there close a single fuse would suffice)

its also best to have 2 of the same battery (so 2 upgraded batteries) but not required. And while u could get a high output alternator or a second alt its not "necessary". U just want to make sure u can keep those batteries in the back charged. hooking up to a batt charger every once in a while wouldnt hurt