I am using an 18650 LiPo cell. But it should work with any LiPo. The reason for the 18650 is historic: I had this running with a Pi-Zero-W (also with some power-management electronics). Compared to the Pico, the Pi needs a lot more current during an update-cycle so the beefy battery was necessary. Since swapping in the Pico I can’t remember when I had to recharge the battery. Self-discharge is probably higher than what I actually use.
