When I was a used tractor dealer and farmed I saw batteries well over 10 years old still functioning even if not near their capacity when they were new. Sulfation occurred on the plates over time reducing their efficiency and capacity....
A battery typically is designed and built and rated to have a certain finite number of Life Cycles with a Cycle being roughly speaking a charge then discharge then charged back up, each time of which uses up one Life Cycle. Sooooooooooo if a battery is well maintained,,,,,,,,,,, not allowed to completely discharge (such as using a trickle charger over long idle periods),,,,,,,,,its electrolyte levels maintained,,,,,,,,,,,,never allowed to freeze,,,,,,,,,HEY IT CAN LAST A LONG TIME
HOWEVER if it endures a ton of Life Cycles consisting of a number of discharges and re charges versus that above, hey it obviously may not last as long. Its NOT good to allow a battery to set long periods in a discharged state !!!!!
Longevity is increased if good maintenance such as keeping the water levels up,,,,,,,,using a trickle charger/battery maintainer to reduce deep discharges,,,,,,,preventing freezing
While sure the design and quality affects longevity and people can brag this or that brand are the best, the BOTTOM LINE remains that a battery has ONLY X number of Life Cycles so the more they are used up the less time it will last.
A TRICKLE CHARGER (or any charger) and not allowing a lot of discharges and re charges are a batteries friend ...
John T NOT a chemist or battery expert so no warranty but believe this to be true, if not maybe an expert can enlighten all of us and lets see if others agree ???