I got one of those Leed's USB power bank from my apartment building during a planned power outage. It blew up when I tried to charge it. There wasn't a whole lot I could reverse engineered from the dead parts. There was a 5-pin and a 6-pin chips and a bunch of passives. My understanding is that it uses an inverting buck boost converter for both charging and output as the VUSB pins of both the USB connectors are connected together.
I finally got around to rebuild it from scratch this weekend with what I have on hand. The parts I have were from aliexpress before the big chips shortages. I use a LTC4054 Li-ion charger chip and a MT3608 boost converter.
The charging rate is limited by heat dissipation on a tiny single sided PCB. The output current is limited by the Schottky diode, inductor and battery discharge rate to about 1A (or slightly higher) or so matching to the original power bank.
|Populated PCB (I only have 1A/20V Schottky diode.)|
|Modified connector to sense presence of USB plug|
|Red LED = Charging|
|Green LED = Operating. Brightness proportional to load|
Yellow is when both are connected, but that doesn't usually happen as the connector spacing is too closed together.