I have just replaced my first set of Envelop AA batteries, ten years after I bought them.
Around 10-12 years ago I was I doing a lot of underwater photography. High capacity, low-static-discharge AA batteries were pretty new, but an absolute must for digital strobes. I'd swap 2 sets of 4 in each one of my UW strobes almost every other dive, as blasting tons of light around the bottom of the sea takes a lot of juice. Sanyo's Eneloop batteries were the only really choice.
Low Self-Discharge batteries are pretty amazing. Not only do Eneloops hold their charge if not used for up to 10 years, but the fact that they discharge while not in use so incredibly slowly means the batteries also stay healthy much, much longer. Whenever one starts to get a bit flakey, I run a refresh cycle on my charger. After a decade, finally, a few have shorted out.
Over time I stopped diving as much, and Panasonic bought Sanyo. My batteries started to be used for everything around the house. I've had them in remote controlled cars, planes, head-sets, remote controls, flash-lights… you name it. These AA's were in constant service for nearly 10 years. Of the 16 I originally purchased, 8 are still in service and charge up to 1988 mAh.
Eneloops are pretty amazing!