• (for a conventional wet cell battery) Only two things I know of that will "bulge" a cell; freezing or frying. My guess is the cell is shot. Do you use a tender? They are great for covering up bad cells... for awhile. I'd also suggest you consider an AGM battery upgrade. No acid spills and more capacity. dmemt #1464 • (for an AGM) Just replaced my AGM battery (in a Classic, 2.5 years old) - while I was doing my service, I saw the telltale sign of a bolt covered with that white powdery stuff caused by leaking battery acid. Sorry - when they get a bulged case that cracks, they "seep". What caused it to bulge? Got me... typical voltage regulator overvoltage (common to Classics - see VR FLAY in FAQs) or a combination of high mile days across the Great Plains in 100F+ weather in conjunction with the location nearly atop the muffler pipe?