I think I've always been lucky with batteries... the one in my '07 GC2310 is still going strong and my '05 TDI still has it's original battery; use the tractor year round, now has about 350 hrs... and I think I MUST be on borrowed time, but the Gill G-35 in my PA-22-150 is dated (with magic marker) as July 2007, but still holds a charge well -- or seems to, at least. Must be some kind of record, I think! (Right now it's in my nice, warm basement at home...)
I'll keep in mind that Interstate MT-51 for the little red beast... and, wunnatheezedayz, I'd love to replace that Gill with a sealed glass mat battery... but then they say I'd better upgrade to a solid state regulator if I do. (At least I only have one to replace, Ray!) WBB