The 5V pin only works when there is a 5V power supply from the USB connector.
This is the way how we designed the board.
If you need 5V from a battery you need to connect an external voltage booster.
The battery is made for 3,7V (which is 4.2V fully charged)
You cannot attach a battery with a higher voltage then 5V when it's fully charged.
A rechardable lipo battery never has the same voltage. 3,7V is the nominal voltage.
3.3V is empty, 3,7v = 50% and 4.2V = 100%.
When no battery is connected, you should measure 4,3V with a multimeter.
4,3V is the charge voltage.
The maximum voltage is 5V, 2