I remember the advise used to be deplete to 80% charge then store batteries in the fridge...batteries now are better and cheaper, thank goodness!
For the most part, canister light batteries now have so much extra capacity that even in 10 years they should still be fine. My strobe batteries are nimh, and I store them without re-charging, then charge night before a dive. They are 10 years old and for the most part, still working ok, but they are getting long in the tooth. With the nimh, I would top them off if I didn't use them for more than 3 months. For the lithium canister lights, I would charge if I didn't use them for 6 months.
My computer and rebreather batteries are disposable lithium that I toss based on hours of usage. I re-use them in my home door lock because I take them out of service with life remaining.
The only batteries where I notice any degradation are my handheld primary 18650 cells. After 1.5 years I just bought newer higher capacity cells to eek out another few minutes of burn time and keep the old cells, which are still functioning at 90% of new capacity or more, for backups or days where I need more dives but can't recharge in between.
The only batteries to be careful with are disposable alkaline, like in your backup lights or computers. Those leak and destroy stuff. Lithiums are way better, more expensive, but how expensive is replacing your light because battery acid destroyed it?
Outside of scuba, my car lithium pack I recharge about every 3-6 months, when it drops to mid 90's on charge. It still jumps my v6 engine at 90% but it's a good time to inspect. Those are stored in high heat and I think every 3 years I would replace them. Motorcycle battery gets completely flat if I don't drive for more than 1 week, so I leave it on a maintainer.
