Hi,
I am using this stepup board for an ePaper project, where I need 5V for runnning the ePaper. The ePaper will hang in a frame on the wall, where I have no direct power connection, so I needed to do some power optimisations wi deep_sleep which works fine.
https://de.aliexpress.com/item/1005005662093377.html advertised as
5V Typ-C DC-DC UPS Step Up Boost Converter Modul 15 W 3A 18650 Lithium Batterie Charger with UPS
The whole setup works fine for my case, but I have the problem, that I cannot determine “upfront” when the battery is running out of power, so that I can recharge it early enough. Having a timer as right now is “more than nothing”, but pretty close to “nothing”. As I do have som free GPIO pins on my https://www.waveshare.com/wiki/E-Paper_ESP32_Driver_Board still “free”, I hoped to be able to have a battery empty detection by “somehow wiring” those two together 
I bet everyting is already on the board, so I could “avoid” things like suggested here
but I cannot “see” where I can get the battery information from my used board.
Does anyone with more knowledge have an idea, if (and how) this might be possible. Also of someone has another hardware powering solution idea where I can get this information, I am open to anything else.
many thanks in advance
Juergen