Think your issure is that battery was designed for a UPS, not as a power soure are a starter. I tried batteries from a battery store, not good results. The price is great. Able to start your engine, questionable. Wasn’t designed to be rattled around in a kart. Very short life cycle. Comet lists an orginal replacement battery. It will only be heavier on your wallet. But it will turn over you engine and it will last.
LAD Specialties customer / tony kart / rotax / kt100