Thank you very much for your help. I will give it a try.

@felmue Seems like you're right. In the meantime I charged the battery to almost 4V and now it can start on battery almost every time I try. I guess when battery is 100% full it will work fine.

And yes, when startup fails it just stays off without boot loop or anything like that. LCD and green LED inside just blink for a sec and it is off. Just like there is not enough power.

I just tried running on usb without the battery (removed bottom2) and everything works fine. Both nbiot modem and gps are performing as expected.

Yes, I know about this thing with connecting external 5V/12V directly to the module but there I have another problem:

When I run it on usb/battery and call M5.shutdown() function (or press the button) everything shuts down (including com.x modules) which is something that I expect.

When I run it on external 12V and call M5.shutdown() or press the button then only Core2 is shut down. Other com.x components are still running and I don't know how to switch them off.

Also, if I plug out the 12V then com.x components are off but Core2 stays running on battery and I am also not sure how to handle this. That is why powering via USB is perfect solution because when I plug the usb out then Axp.isOnAC() is false so I can call shutdown() method which will switch everything off.

Hi there,

I've made a following setup:

Core2 - (removed factory battery)
Com.x Nb-IoT module
Com.x GPS module
Bottom2

When I power it up using usbc on core2 everything works perfectly. When I disconnect usbc power source it continues to work on battery (which is in bottom2) and this is also fine.

The problem is when I switch it off and try to start it only on battery. It starts only for a fraction of a second then turns off. I tried the same thing with both com.x modules disconnected and in that case it powers up normally.

Anyone knows maybe why it cannot start up on battery but can run on battery once it has been started using usbc power and how to circumvent this situation?