Thanks so much for this thread! This weak my battery broke, it might die soon. It's disappointing as it was in a very good condition, then I haven't been using the reader for a few months, taken it out of the drawer just this weak. The battery went down to 4x% (46% I think) and suddenly the reader stopped responding. When I connected the power adapter it started charging and booted again. Now I can see that it dies at 67%.
Buying replacement battery
Woohoo, some company started selling replacement batteries. I've ordered one. Once I'll get it installed I'll let you know how well it performs
https://www.aliexpress.com/item/1005002608197116.html
I keep my fingers crossed, but sometimes such replacement batteries have poor capacity or/and longevity. I just know nothing about the brand.