ESPHome, Heltec Wifi Kit and a battery

I have a number of Heltec ESP32s around the house connected to USB power sources. In the garden I have 3 of them with solar panels plugged in the USB connectors and a battery plugged in to the board’s LiPo connector. This works well - USB charges by day, battery runs overnight and even in the UK with our unpredictable weather I get 24/7 reporting most of the time.

However, I would like to monitor the battery. I’m not looking for any degree of accuracy, in fact “charging” and “discharging” would be great. But I can’t find any clues on how to do it. I’ve found documentation on how to collect voltages from ADC readings on certain GPIO pins but as far as I can tell the charging process of the board doesn’t expose anything that I can query.

I did find one - just one - bit of Arduino code on GitHub that implied the battery’s voltage can be read from GPIO10 but I can’t get that to work. I found another article that indicates installing resistors to enable the ability to read the battery’s voltage which I think is unlikely (note: I’m not confusing it with a voltage divider).

So I thought I’d ask here if anyone’s got it to work or might have some pointers?