In 4.9+ xfce4-panel the icon-like plugins typically occupy 1 row to allow multi-row panels/deskbars. The icon of the battery plugin looks very large in comparison. Also, the panel has two vertical modes ("vertical" and "deskbar"). Battery plugin looks OK in the "deskbar" mode (horizontal orientation of labels) but is inconsistent with other plugins in the "vertical" mode.
Created attachment 4134 A patch implementing these features
Created attachment 4135 As before, fixed an icon size error.
Applied in http://git.xfce.org/panel-plugins/xfce4-battery-plugin/commit/?id=1a45c5301f018ac89cdfb8479c3d29fd0e1412b4 http://git.xfce.org/panel-plugins/xfce4-battery-plugin/commit/?id=fb5ae31d9efa8a8af673da466851d17642b6a93b & http://git.xfce.org/panel-plugins/xfce4-battery-plugin/commit/?id=baaedc27dcb5d9d0a9df0e43e71cffe2fb380d6f