Because mastodon is the Linux of social media. One day it will be ready for the average user…

Define ‘hold a charge well’. There is a lot of conflicting information about NiMH v Li-ion regarding self discharge rates and not much in the way of hard facts. Probably depends a lot on brand/construction of the cell. But even a good one will be (almost) flat if not charged for a few years, and possibly dead (as in cannot be charged anymore). Single use lithium cells last longer (10 years or more) but are expensive and not rechargeable.