This is a re-post from GitHub. Please also see further comments there. The bug is still present in 2.530.
Description of bug/feature request/question:
I have the Battery widget configured to only show charge percentage next to the icon, but not the remaining time. This works as expected when running on battery. When I plug in the power cord, however, the percentage switches to either "?:??" or "∞", depending on whether the battery is charging or fully charged. If I unplug the cord again, "?:??" is first shown, then after a few minutes it updates back to showing the percentage again.
Also (somewhat less importantly), the battery icon changes to "half empty" as soon as it first updates back to showing the percentage; but "half empty" + "100 %" seems rather inconsistent. 
(It does show a full battery icon before that update, i. e. immediately after disconnecting the power cord. Apparently, the gradation of that icon and its correlation with the percentage value could be improved.)
Affected input device (e.g. MacBook Trackpad, Magic Mouse/Trackpad, Touch Bar, etc.):
Touch Bar
Device information:
Type of Mac: 15" MBP 2017
macOS version: 10.13.4
BetterTouchTool version: 2.422