/usr/share/notify-osd/icons/Humanity/scalable/status/notification-battery-low.svg is in notify-osd-icons 0.8+15.10.20151016.2-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/notify-osd/icons/Humanity/scalable/status/notification-battery-020.svg