Battery Life has shortened

I had this unit (GPD Win Aluminum Z8750) since July. My battery life has shortened by over one hour, with the Battery Wear indicator though third-party software showing it at 55.15%. This was not occurring last week, where I had more than 3 hours of battery life while gaming. I have no idea if the battery itself got damaged, or if it is just an erroneous reading. What exactly should I do to rectify this issue, short of having to purchase another battery?

You can email to kendyz@gpd.hk.

You can get one from https://www.ebay.com/itm/Sunda-8448104-GPD-Win-Battery/312033540512?hash=item48a6a5f9a0:g:HPAAAOSwj99aQ~7Q.