Note: Be aware that working with lithium-ion rechargeable batteries is dangerous. This is not a step by step tutorial. Do not base your work solely on these instructions.
Introduction:
I bought a few very cheap Powerbanks without the 18650 li-ion cells. I had some left from a previous project. The problem: the internal charger is quite slow.
The battery charging current is limited to about 2A according to the MP5043 chip datasheet. I have 4 cells @ 3400mAh capacity, then charging the whole set at full voltage is going to take around 6.8 hours. We can do better.
Modifications:
The goal is to bump up the charging current to let's say 4A. We could go higher but I will use the material I have: connectors (2mm in diameter) are rated at 6A and the fuse at 5AF. The switch is good up to 10A.
The modifications are fairly easy. You have to desolder the 2 contacts B+ and B- (see schematics).
The new components take the space of two 18650 cells.
That works like that: To charge, you flip the switch to "0" position and set your charger to 1s.
To use the powerbank, switch to "1". That reconnects B+ and B- to the board, the whole module is powered and you have voltage at the USB ports.
Don't charge the cells in position "1". You will feed the board with whatever voltage you set your charger at.
Note: You always have the battery voltage on the 2mm connectors whatever position your switch happens to be. Keep that in mind.