Mine shut down unexpectedly last night with just a 0 on the LCD. As I was going to bed at the time I just power cycled it and everything worked again.
Checked their website today and it seems this error means internal fault.
So it seems the writing is on the wall.
I ordered a more expensive unit from a reputable manufacturer (almost twice the price) to replace it. Just hope it holds out until Tuesday when the new one arrives.
Also amusingly saw they now sell an Amazon Basics UPS
yeah I'd trust Amazon Basics for a lot of stuff, but not a UPS.