I'm running KDE from master and I've noticed that for quite some time the battery widget does not properly update the displayed battery percentage. It happens mostly randomly - I wake up my laptop and it just sits there showing me 99% all the time. Sleep. Wakeup. It works ok. Sometimes. plasmaengineexplorer seems to be always showing the correct value though. So just displaying the percentage actually does not work - both on the plasmoid icon in systray and in the popup. Re-adding the plasmoid (or adding a new one) does not solve this. I can provide any further debug/testing if needed.
dupe of 272371?
Actually I haven't seen this for a while with 4.8/master. I close this for now and reopen if this is still valid.