i was looking around and found a video on youtube and it showed that running extra betteries wont help since your stock alt wont recharge them properly as you play music and soon it will die on you for over working, if you go that way make sure you charge your batteries everynight so it wont harm your stock alt, also look into getting a HO alt they go for 450 a good battery goes for 359 if you need 2 of them then the HO alt would be the way to go