Mine stopped working altogether. No sign of life even with the power plugged in. I had tried the "reset" steps I found on the internet (holding big button down then plugging into power) and also a USB cable still with no lights or signs of life.
I disassembled it, unplugged the battery, plugged it into power without the battery and it worked. Then I unplugged the power, plugged the battery back in, and plugged it back into power. It fully charged in a couple of hours and the battery measured 12.58v (with no load) after it was fully charged. It works fine now.
I think the battery is probably three 18650's in series with a protection circuit.