SilentAV8R said:
In essence, the "Useful" capacity of lipo pack is actually 80% of the full rated capacity. Discharging below that can cause issues with recharge and may kill the pack long before it should normally die.
Battery health isn't a hard cutoff at 80%. A battery discharged to 75% is going to be marginally "healthier," all else being equal, than one drained to 80%, and one drained to 80% should be slightly healthier than one drained to 85%. With hobby RCs, "all things being equal" is a tall order. People who are assiduously tracking their battery usage and health will probably have healthier batteries draining to 90% than someone who drains to 80% but doesn't follow best practices, etc. Impact on long term health also depends greatly on discharge rate in relation to C-rating, temp of discharge, and other factors independent of whether some magical 80% mark is maintained.
I don't we fundamentally disagree in principle, but calling 20% completely depleted wrt to useful power is definitionally idiosyncratic and makes it a bit harder to discuss battery usage in common terms.