mate-power-manager still seems to use the old gnome-power-manager gpm- prefixed names for battery icons. Also, the tray and the power statistics window each prefer different sets of icons (see the bottom of this post for details). These are not used for any other desktops and are not provided in many modern icon themes. They are probably less likely to be provided as time goes on since other desktop environments are using the same naming standard.
Other Desktop Environments
Gnome, Xfce, and Cinnamon use a new icon naming standard. battery-level-##-symbolic for more granular icons in places like panels and trays. And as an example used for less granular places, battery-caution -- this style is the Upower standard and is currently the most common in icon themes.
Granular naming adopted by other desktops (there is no non-symbolic variation):
Problem
mate-power-manager still seems to use the old gnome-power-manager
gpm-prefixed names for battery icons. Also, the tray and the power statistics window each prefer different sets of icons (see the bottom of this post for details). These are not used for any other desktops and are not provided in many modern icon themes. They are probably less likely to be provided as time goes on since other desktop environments are using the same naming standard.Other Desktop Environments
Gnome, Xfce, and Cinnamon use a new icon naming standard.
battery-level-##-symbolicfor more granular icons in places like panels and trays. And as an example used for less granular places,battery-caution-- this style is the Upower standard and is currently the most common in icon themes.Granular naming adopted by other desktops (there is no non-symbolic variation):
Upower names -- all of these are also used with the
-symbolicsuffix:Solution
For the tray/panel icon, I think preferring the
battery-level-names first and falling back to the Upower symbolic names would be the best solution.For power statistics if symbolic icons are not preferred, prefer Upower non-symbolic first, then fall back to the other two symbolic names.
And then if needed the gpm- icons as a lowest-priority fallback.