There are anecdotal reports of solar Casios going 20+ years on that battery. Which makes sense given that its capacity should just gradually reduce over time - and when you start with full capacity that can drive the watch for over a year (assuming no backlight etc), even if it drops to half that, it's still very much usable.

Maybe keeping it charged is key. I have had mine for almost 10 years.

Mine stopped holding a charge somewhere around the time you got yours. I recall picking it up at the PX in the summer of 2003...

However, I will dig it out and see if it can be resurrected.