My Xtorm recently still showed 100% even after 2 months of non-use. There definitely seems to be something wrong with it. Charging does indeed take a long time, it's also a powerbank. So it's kind of to be expected. Since something is obviously wrong with yours, it will probably take a little longer.

My powerbank keeps the charge very well, the loss is maybe in the percentage range after days. Something must be drawing power, this can also be the built-in fan when it is switched on.
Charging actually takes a long time, with 23Ah it's like charging 6 smartphones. I do this over night each time.