Batteries

All that's required is a salt and: battery.

"When a good cell goes battery."

List

https://www.eevblog.com/forum/projects/coulomb-counter-ic-for-coin-cell-products/ - not many options for measuring current out of a coin cell, without drawing a notable amount of current.
https://www.eevblog.com/forum/chat/rechargeable-alkalines/ - It turns out that alkalines are (or once were) rechargeable. someone would need to investigate.
https://www.eevblog.com/forum/renewable-energy/are-deep-cycle-lead-acid-datasheets-a-scam/ - Uncertainty and Doubt with Lead Acid batteries and 'deep cycle' longevity. Someone suggests that the chargers are to blame - not the batteries. Some long term testing is in order, I think: with a load and some lead batteries (i would be you could use small ones, you probably don't need to use car batteries. start small...).
https://hackaday.com/2025/01/10/aa-battery-performances-tested-so-get-the-most-for-your-money/ - "It’s always been Eneloop NiMh rechargable, and Energiner Max or Lithium. There have been candlepowerforums threads on it for decades. Most people just use a OPUS BT-C3400 to test AA, AAA, C, 18650."

A bit of semantic nonsense, but technically a battery is made up of cells. https://www.eevblog.com/forum/projects/biggest-battery-capacity-for-22-x-22-mm-case/ - cell vs. battery (cell is a single, battery is a collection of cells)

3.5 or 3.6mah is the highest single 18650 cell you can buy. a couple amusing anecdotes.