Battery objects are casted DeviceInterface objects and those are
owned by Solid. deleting them outside solid means they will end
up as dangling pointers inside Solid's global static objects.
when switching away from the energy KCM the qml engine would
get cleaned up as part of the KCM destruction, qml would then
sweep up the Battery object and corrupt the solid internal
to prevent this, explicitly mark Battery objects we give to QML
as owned on the c++ side.