Check Engine Light????

Ok guys, heres the deal. I have a '90 5.0 hatch that has been in a garage for the past two years since I bought my '03. I found out ins is only like 60 bucks a year extra to have both cars on under my name, so I am going to go that route .
I do have a concern though. I am pretty sure I have at least 1 or 2 cattalytic converters that are toasted. It has the stock manifolds and mid pipe, but has flowmaster 40s welded in. The last year I went to get it inspected it wouldnt pass and I had to put something called guarenteed to pass in the gas tank. It worked and I got a nice new inspection sticker. I never had trouble with a check engine light. I went to drive it around some last weekend and on my way back the check engine light popped on. I put it back in the garage, and started it up again, no engine light . The battery is basically dead, we had to jump it both times to get it started. I am buying a new battery of course soon, but I am curious as to what could be causing the light. Would the blown cats finally make it come on, or could it be sensing the battery is dead as well . Im at a loss here guys. As soon as I get it here to my house its going in for a new mid pipe, and lifters installed. Its got a lifter sticking as well I know that for sure. Any clues as to what could be causing the light? I didnt feel any misses or anything driving it around. It felt great honestly. I didnt take it above 45 though so I dont know how its going to do on the hw coming here to Raleigh.
Thanks guys!

Thanks