I think the best way to fill up the battery is to use regenerative energy from braking that could have been wasted anyway, rather than using the engine to charge it.
I'm just saying that there are times where a slight lift or push of the throttle makes all the difference in whether the ICE is charging the battery without a significant change in the FE gage. Without the Energy screen you are not aware of this mode.
Not a big deal but it's a tid bit of knowledge to know that when the ICE is on and driving the wheels there may be a side benefit of the battery being charged because the ICE is generating more HP than is needed for the current propulsion.

I agree that the braking is the BEST (more effecient) mode to charge. BUT if you want you can "force" some battery charge at times when you are using the ICE and there may be situations where that is beneficial.