I went to upload it and found it sitting there already! https://github.com/meshtastic/Meshtastic-device/blob/master/docs/hardware/heltec-wifi-lora-32-v2-915.pdf
I’m not sure how it would work compared to other boards that report the battery state, but when the Heltec device sleeps it will disable Vext (turn off screen) so the battery voltage can’t be read.
It also would appear GPIO13 would see full battery voltage as the divider isn’t being pulled to ground…(doesn’t sound great, maybe the 220K resistor saves it as it is already what is happening). I think the input limit is VDD +10%. The Heltec uses a different divider ratio so I’m guessing something would have to change there too.
I have added it to the Issues in Github.