Adding a Battery and charging module
I have used a 3.7V Li-Ion 700mAh Battery, a TP4056 Charging module with protection IC and a CKCS BS01 step-up module.
TP4056 with protection chip
The CKCS BS01 Step-Up step-up module has 2 resistors (A and B) on the front side. Remove both of them to set the output to 5V. You can use a soldering iron to do so.
Connect everything as shown in the charging circuit:
