My friend was going to throw away this LED lantern because the battery pack was nowhere to be found.
I looked it over and saw potential. The original pack was 6V and it made me wonder how it would perform as a USB light. I was pleasantly surprised at what I discovered after rewiring the unit.
I believe the LEDs are fed regulated voltage, because I tried this at several different voltages from other power sources and there was ZERO increase or decrease in output. However, when I got just below 5 volts, it began to flicker. It seems that 5 volts is the absolute lowest voltage it can run stable at.
As it turns out, this is the very voltage of almost all USB battery banks. They maintain a constant voltage throughout their cycle due to the needs of the devices plugged into them, as well as a DC - DC converter in most of them.
The thing also draws so little power, that I have to press the button on some of my power banks in order to get them running. The USB powered fans I run draw 250mA, but this lamp, I think, draws quite a bit less. I don't have my meter, but I would venture a guess of about 100mA.
This is a pretty commonly available light, so you might be able to do this too if you have lost the battery.