Misleading battery status

After fully charging the battery is never showing a full bar and it **very** quickly deteriorates from green to orange. I am not sure whether this is due to my device or a more general problem, e.g. rounding errors.
Using Specter Shield with battery.

Related to this, it would be a better UX to see a charging symbol when charging the DIY while on. Or is the charging too minimal when on? @stepansnigirev

Start by reproducing the battery display behavior on a DIY using Specter Shield, both after full charging and while charging with the device on. Trace how charge levels map to the bar colors and how charging state is detected. Done means a full battery shows a full bar, the colors do not deteriorate unexpectedly, and an appropriate charging symbol appears when applicable.

Written by the indexing model from the issue text.