Currently, isInDefaultPowerProfile is set to false when the PowerProfiles daemon is not installed. This causes the batterymonitor system tray entry to remain stuck in the active state, which is rather annoying.
This happens because defaultPowerProfile, which is set to "balanced" when configuredProfile is unset, and activeProfile, which is blank when the daemon is missing, are not equal.
This patch sets isInDefaultPowerProfile to true when activeProfile and configuredProfile are both unset. On my systems with Plasma 6 installed, this fixes the behaviour of the batterymonitor widget and correctly puts it into passive state. On systems with PowerProfiles daemon installed, this should not alter behaviour, because it only triggers when activeProfile is blank. None of my hardware supports it so I was unfortunately not able to try.
If there is a better solution possible, please let me know, and I'll open a bug report or update the merge request.