Battery overheating

I bought a used '99 Caravan SE. It apparently has a problem with overcharging (over heating) the battery - It's caused a fairly new battery to over heat and push fluid out of the cell cap, there's also corrosion (splatters) under the hood from past problems. The parts store that sold me the battery tested the alternator, couldn't find anything wrong, and begrudgingly replaced the battery free of charge...they've got me convinced that it's the van and not the battery...any ideas??

I bought a used '99 Caravan SE. It apparently has a problem with overcharging (over heating) the battery - It's caused a fairly new battery to over heat and push fluid out of the cell cap, there's also corrosion (splatters) under the hood from past problems. The parts store that sold me the battery tested the alternator, couldn't find anything wrong, and begrudgingly replaced the battery free of charge...they've got me convinced that it's the van and not the battery...any ideas??
Hi Nukl,
I have a 99 grand, had it since new. I have had this problem with my old 88, but not in the 99 or my 01. The alternator must "see" the battery's voltage through the wiring. If the ground wires are corroded, the alternator will think the battery need to charge and will put out more voltage than actually needed. Be very thorough in cleaning the smaller terminals attached to the battery ground terminal and expecially the ground path from the alternator to the chassis at the mounting point. In my old van, the problem was in the chassis ground to the body. You can check the voltage at the battery with a decent tester. It should be around 13.5 volts with a fully charged battery. Over 14.5 volts will start to overheat the battery. Hot weather and long trips will accentuate this problem. Good Luck.