@paul-thornton ... and in the boot.py file I have this code: # boot.py -- run on boot-up import os from machine import UART uart = UART(0, 115200) os.dupterm(uart) #disable the wifi radio from network import WLAN wlan=WLAN() wlan.deinit() #disable the bluetotth radio from network import Bluetooth blt=Bluetooth() blt.deinit()

@PaulM You might want to look into firmware version 1.19. At the moment it is still in beta, but it adds the option to use LittleFS instead of FAT as the primary filesystem of the internal flash. This prevents data corruption even in the case of power loss during write operations.

@toppert Some of power banks can support low current mode. Some of tem must be turned in this mode by special press on the button, some work from the start. But many do not support low current mode at all. E.g. "Mi" power banks support this mode - but as @seb say already it is super inefficient. You can got longer time from battery then from powerbanks.

When working with unprotected cells, a circuit like this should work fine, right? [image: 20170825235011-yimzrv24.png] With a MAX6430EGUS+T, the ~LBOH output turns low when battery voltage is <3.3V, while ~LBOL turns low when battery voltage is <3.0V. That should trigger the left MOSFET and turn off the entire circuit.