Recently, a friend of mine has discovered two power-manager icons in her notification area. This had confused us both for a while, until we noticed that the second icon was for her Wacom wireless tablet. To avoid this confusion, it should really say the battery name in the tooltip and notifications.
This bug has been fixed in git master (and will be part of the next release). There is now only a single plugin that shows all other devices in a menu instead of separate trayicons.