T-Man
A practical rule of thumb for a bike battery (sealed) would put it's life span at between 3 and 4 years. During this time you can keep it in optimum condtion via the battery tender. Even down south there are down times in riding because of inclement weather, vacations, sickness etc. A battery tender does very nicely here and there is no need to remove the battery, especially if your bike is in a garage. Personally, 3 years is my arbitrary limit on keeping a battery. Beyond this I would never fully trust it's dependability. Having you'r bike battery go dead on some remote road far away from home and help is just not worth it to me. With a car I might wait until I experience some problems, difficulty starting etc befor dropping in a new battery but with my bike, no way. It just is not worth the hassle.