All the flashlights at my home are powered by ~14 year old 18650 cells scavenged from old lenovo battery packs (I think mostly x61 batteries). Usually the case

All the flashlights at my home are powered by ~14 year old 18650 cells scavenged from old lenovo battery packs (I think mostly x61 batteries). Usually the case is that one cell in a 'dead' battery has far lower capacity, and might only run a flashlight for 20 minutes (which is still useful, though I dispose of those). The other cells are comparable to new ones in capacity (maybe they're 90% or whatever of their original). We often have a distorted idea of lifetimes and reliability because absent real scarcity we're overly prone to discarding things which can be fixed (e.g. using 5 bad laptop batteries to make four good ones) or are still usable. If you have no other source of light at night a flashlight you can only use for 20 minutes is still a life changing transformative device. One could imagine searching for battery technology with much longer lifetimes. But I think you'd be better off with the best batteries you can find out of thousands of lithium cells ambient around you than just a few 'super batteries', esp if you're only talking about your lifetime or the lifetime of your children.