Using an alternator on a dead/sulfated battery is a bad idea. It is not a battery charger its a maintainer. I would use a ctek 3300 or 7002 or if money is an issue a schumacher xc-6. XC-6's can be bought at wal mart for 30ish bucks but the 70ish dollar 3300 will more than likely do a better job. Only question is what stage the sulfation is in. If it is crystalized it is a lost cause. This is why it is important to keep lead acid batteries charged.alright cool. until i can get ahold of one, is it a bad idea to try to charge it off the main battery?