I'm not sure if this feature should be implemented in ManicTime because it may not be related to work productivity.
However, in my case, I would like to be able to distinguish in the Computer Usage timeline whether the laptop was being used with battery or plugged.
This would be useful, for example, to see the exact moment in which you changed your working location.
Also, it's useful to estimate the battery wear level, although this is not probable the aim of ManicTime.