I now that the big problem for motorcycle batteries is, because of their smaller size and the need for cranking amps, the lead plates are thinner, which is why they do not last as long
Vibration plays a role in lead acid batter longevity too.
The largest lead acid battery I have seen was a redwood water tank , tar lined, filled with an and water H2S04 solution and had the plates lowered into it by a chainfall above the tank. The plates were serviced/inspected annually for degradation and replaced as necessary. That battery was in use from about 1910 to 1979 and was retired because it was considered to dangerous. There was no vibration associated with that battery and it could have lasted forever. Our 3 wheelers vibrate considerably, possible more than a softly suspended Harley and the idea of using AGM Lithium Ion batteries makes sense.
