Critical battery level triggers Log Out dialog, not battery warning dialog
In xfce Power Manager > System > Critical Power
I have "On critical battery power" set to "Ask"
As soon as the critical level is reached a dialog pops up, though it's the regular Log Out dialog,
not the power manager's battery warning dialog:
xfce4-power-manager* 1.6.6-1 xfce4-session 4.14.2-0ubuntu1 xfce4-settings 4.14.3-0ubuntu1
discovered in xfce4-session#97 (comment 50193)