[rotorwrench]

A battery that is used on a daily basis will last longer than a battery that sets up for long periods. It's not enough to just put a battery charger on them. The only way to knock the sulfate build up off the plates to any great degree is to draw them down with a big load like a starter does. Lead sulfate materials that fall off the plates will settle to the bottom of the case and build up over time. Eventually they will reach the bottom of the plates and start to short them out. You can call it planned obsolescence but batteries eventually wear out due to loss of spongy lead from the acidic reactions and sulfation. None of them last forever.

Back in the day, they would rebuild them by removing the tar and old plate set then they would install a new plate set and apply sealing tar.

When servicing a battery, add distilled water to replace water that is evaporated out. If you use battery electrolyte, the acidic content will be too high and eat the battery up. You can attempt to drain them but you can't always get all the lead sulfate materials out. Tar tops could be opened up and resealed but these plastic ones not so much.

The spiral cell AGM type batteries last well due to the way they deal with sulfation but they cost a lot more too. The spiral cells have more lead and spongy lead plate area than the average battery due to the way they are manufactured.