20 years? Try more like the 1960s. NiMH in the 80s.
NiMH batteries are pretty decent these days. Capacities are high, and life is generally longer. You can still get NiCAD as well, the good thing about those is you can stick them on a shelf and pick them up 20 years from now and have a good expectation they'll take a charge if they aren't used up when you store them. Those tend to be a lot lower capacity, however. NiMH AA is 2200mAh for a good one, NiCAD is 600.
Both will still lose life with charge cycles, that's just a problem with batteries. Don't buy them from AliExpress and you'll probably be fine.
I meant the consumer-grade ones. obv!
Thanks for the firsthand info.
NiCADs date to the 60s in the forms we recognize but are from the 1800s. NiMHs first appeared for consumers in the late 80s. Rechargeable battery technology is quite old as far as electronics go.
A word of caution, don't put stuff like this on a shelf and be 100% certain it's going to work years later. NiCAD has the best chance, they're pretty stable devices.
You can make batteries out of metals and common household acids. https://www.instructables.com/DIY-Chlorine-Battery/
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