Created attachment 5507 Panel plugin fixes. (Sorry for merging what should be separate bug reports into one). Neither battery nor brightness plugin currently support multi-row panel layouts. Also, brightbess plugin inverts the slider direction in the vertical/deskbar panel mode. Attached a patch fixing these issues.
Good to see Xfce's plugin expert help us out :) Thanks for the patches, pushed to master in: http://git.xfce.org/xfce/xfce4-power-manager/commit/?id=2b3d589a8464b8913b6afb79658e42d349f94a57 http://git.xfce.org/xfce/xfce4-power-manager/commit/?id=ddf18c85c91d85195f3bc9b046d79295c886e0eb http://git.xfce.org/xfce/xfce4-power-manager/commit/?id=07fd60cd9f5088f5653a7f3a579e6ef4fdbea832