GLE 350D what does charging mean?

[EclassAnt]

My W212 E is in for some work and the dealer has kindly lent me a almost new GTE 350D while the car is sorted. Of course it's come with no manuals or anything
Slap in the middle of the dash (I can't see the speedo or rev counter when the steering wheel is in a good position) is what appears to be an economy gauge, although I understand you can change all this around if you want. Most of the economy gauge makes sense but if you back off it goes past 100mpg and has a section saying "charging". Charging what? it's not the hybrid model it's the 6 cylinder diesel. Anyone any ideas?
I can't find any sensible manual for the dash board online. But then given the number of things the bit in the middle does I suppose a manual would be bigger than the car and need changing every Tuesday when the software updates. The quick start manual tells me how to pair my phone but not what any of the controls do.

[quinny100]

It's shows when the car is recuperating kinetic energy and using it to charge the 12V battery when coasting - this is effectively free energy for no fuel consumption penalty.

If you select Eco mode you'll probably get Gliding Mode - this disengages the transmission and effectively allows the car to freewheel along with the engine at idle speed. On a flat or slightly downhill gradient you can coast a surprisingly long distance in this mode.

[EclassAnt]

Thanks quinny100, that makes sense. Never thought of the alternator taking much power, but I guess every little helps.
Oh and I'd got the model wrong, it's a GLE not a GTE - Duh.