Context: Several sensors require cr2032 cells (cadence, speed, temperature, HRM, etc.) so I wondered about the possibility of relying on rechargeable cells (LIR/ML).
Experiment 1: recharging. Failure. I've purchased several lots of ML/LIR cells and chargers. Mostly fails with ML, and very unreliable results with LIR. Not worth the trouble.

Context: May as well use low power CR2032 see-me taillights. Very cheap and surprisingly efficient. Benefit over rechargeable USB is that you can swap in fresh batteries if the light goes dead in the middle of the night.
Experiment 2: Decathlon sells small ("turtle") taillights nominally rated at 44 hours in blinking mode. I've set two on my desk, one fitted with the provided no-name coin cells, and another with Pro-Cell batteries, rated at 745mWh, vs what I assume to be 650mWh for run of the mill 2032. The no name powered taillight blinked for 5 days (120h) whereas the ProCell lasted more than a week (170 hours). I'm impressed.

Takeaways: Rechargeable 2032s are unreliable. ProCell batteries do work (much) longer in this use case. I've retired my old taillight and will carry a pair of turtles on my back. I conservatively plan on an average of 8h/week with taillights on. Looks like a pair of CR2032s would get me going for close to 6 months...