Board loses power

[Woutch]

Dears,

I left mij V1.1 charging overnight, but put in sleep mode.

When I returned in the morning, I was not able to get the module out sleep mode. I pulled the battery and reseated. (Battery voltage : 4V).

The red led on IO4 burns for 1 second, then goes out. During this 1 second the board works. But when the light goes out, I loose the ESP connection, also not able to connect over serial.

What can I do to revive the board? The 1 second is also too short to reflash something, I tried, but always looses power at around 14%.

Tried also long pressing the buttons or button combinations, no luck, always after 1 sec everything goes dark :-(

Thanks!