My Astro Is Having A Hard Time Starting, when i turn the key on and push the gas pedal the ses light turns on and off, cause my van to sumble starting or ideing. what would cause this. i just changed spark plugs and injeters

I purchased a Autocraft Titanium battery from Advance Auto Parts about two years ago. It has a three year replacement on it. Anyways I noticed today that it had recently leaked from the vent, melted the handle and some of the plastic housing down the side of it. It also melted the housing on a battery separator that was mounted underneath it for my deep cycle battery for my camper, I'm not sure if it works anymore, was melted pretty good. I was wondering what would cause this? The truck still starts fine ('97 Chevy K1500) and the dash gauge for the battery doesn't show any overcharging. I spoke with a guy at advance and they said I would need to bring it in so they could test the battery and see if its still good to issue a replacement. Wouldn't a melted housing constitute a bad battery? Also what are the chances that they would replace the damaged battery separator if it is due to a bad battery. I can understand it would be my problem if the alternator is overcharging the battery. I spoke with the assistant-assistant :) manager at advance and he said call back tomorrow when the assistant manager will be there.