Anything that fits into the battery tray and is marine rated. AMG is better than traditional, but as this is a little jet ski engine, any big battery would be plenty for it. Sorry I can't give the battery number right now, I'm not home at the moment.
I had a 97 challenger a while ago and I just went to Autozone and bought a marine battery. I wasn't looking for anything special, just picked one up, threw it in and never had a problem.