Unity should act smart and try to conserve power when running low on battery
Unity should automatically make some decisions when running low on battery in order to conserve power. Ubuntu already does this in a few ways, like turn down screen brightness etc. I think Unity should also be made power aware. One thing Unity could do is switch dynamically to the low graphics mode when running low.
We can also add an option to "System Settings > Power" to turn this behaviour off.
I think KWin turns off (or used to) compositing when running low on battery power.