We run batteries for a long time and have been fortunate. Some are 12 years old, a couple are even older than those. I replace one when it starts to say I'm quitting" via the hydrometer and retained voltage - quitting happens infrequently. I've never plugged in the engine heater in winter and, or the first time in 19 years, on a minus 20 morning last winter our Dodge Cummins did not want to spin - "click, click"- and I felt certain that the two Optima Reds in there were not spoiled.. It did not want to spin with help from a booster cable from a Chevy. So, I hooked up a small charger at 5 amps for 15 minutes, then put the charger in "start" mode, and the Cummins fired right up. For some reason, the cold snap that time put the batteries to sleep. They are still in there 7 months later, and doing fine.
With a bunch of 45 to 50 year old vehicles, i do keep a fresh batter (usually a blem from Morco) on a trickle charger and ready to go. The spare "ready to go" has been sitting there for 15 months. Of course, these old trucks/car do not have lights/clocks/computers running as they sit.
Here's the little bit I know. A batter kept up to - or close to - full charge at all times will live much longer. I keep trickle chargers going on all batteries where the vehicle is used infrequently. A battery in which the distilled water level is kept proper will live longer. A battery which has been drained dead - or even near to dead - is difficult to re-charge properly and has seen its death notice. In some cases, very good jumper power from another vehicle battery to the terminals of a dead or badly wounded battery will not spin the starter of the dead vehicle - something goes dead in bat land and that's it. The only cause I've ever seen for battery explosion has been when the bad battery is putting out hydrogen (has no odor) and an errant spark from a "jumping" process ignites the hydrogen. The moment will tend to concentrate your mind. There may be other causes, but I've been fortunate not to experience those.
