Having sysutils/plasma5-powerdevil installed without sysutils/upower seems to be useless -- the 'battery and brightness' tray icon just reports that it isn't aware of any batteries, since powerdevil uses upower as a backend for getting information about the system. This dependency exists in x11/kde-workspace-kde4; but it seems to have been lost with the upgrade to KDE.
A commit references this bug: Author: tcberner Date: Fri Aug 24 17:46:53 UTC 2018 New revision: 477968 URL: https://svnweb.freebsd.org/changeset/ports/477968 Log: sysutils/plasma5-powerdevil: add missing runtime dependency on upower PR: 230693 Reported by: cperciva Changes: head/sysutils/plasma5-powerdevil/Makefile
Committed. Thanks.