I will supply voltage about 7 volt to Arduino pro mini on port RAW. This helps Arduino pro mini measure the battery voltage properly.

I use the voltage boost module.

The module lifts the voltage from 3.7v to 7v2a .

Or module to raise the voltage from 3.7v to the desired voltage.

C2500 Transistor used to turn on / off the charger. 4N60C Mosfet is used to turn on / off power (4N60C mosfet replaces Relay3v3a).