Onboard SH1.25-2 battery interface, integrated lithium battery management system (charge and discharge management, overcharge protection, battery power detection, USB / battery power automatic switching).
Seems like this is only for lithium batteries. Maybe it can run off NIMH batteries but not charge them?
I'm not familiar with that specific board or the charge circuitry in it, but it does, indeed, sound like it's designed for lithium (most embedded chargers are these days unless otherwise specified). You're also correct in that it can run off of any battery within voltage spec, but charging non-lithium batteries would not be recommended.
I wouldn't advise it unless you can disable the charging circuit when USB is plugged in. You may be able to put a diode inline with the battery to only allow current to flow out of the battery, but it would drop the voltage a bit. Still, may not be worth it.
If you really want to use the NiMH batteries, you'd probably be best to run them as a dedicated supply that doesn't go through the charge circuitry (i.e. don't use the battery connector).
More Info: https://rechargemybattery.com/can-i-use-li-ion-charger-to-charge-nimh-rechargeable-batteries/
Thank you very much
Ok I figured out that I maybe can't charge NIMH batteries, but by connecting them to the 5V pin I can run the board off of them :) I'll try it and then report back!
https://resource.heltec.cn/download/WiFi_Kit_32_V3/HTIT-WiFi%20kit32_V3(Rev1.1).pdf Lithium battery(≥250mA) min: 3.3 typical: 3.7 max: 4.2
So I guess I could try to run it on three AAA batteries. Worst thing to happen is I fry the board, which was only 10€. I'll wait for a reply here though
Edit: I meant AA batteries
My guess is that you could power the board, but charging will end in disaster.
Nimh isn't as energy dense as li-ion as I recall? So an 18650 is probably a better bet.
Yeah my plan was without charging. But I found another solution anyways :)
A community to discuss Meshtastic (https://meshtastic.org/docs/introduction)