Hopefully this will clarify.
In electric mode only the charge generally only goes down when driving (although you will recover a small amount through regen).
When working in hybrid mode you can set a reserve level in the battery settings so that it will not drop below your set limit. This is to keep some electric range for low emission zones. When this set point is reached then the petrol engine only operates.
Now if you have no or low charge and running in hybrid mode (i.e. petrol engine active) and set this limit above where the battery currently is then the battery will gain charge. It must do this at the expense of fuel consumption so the benefits are limited.
When doing this the hybrid mode on the dash changes from a picture of a battery with sideways chevrons changes to one with chevrons facing upwards.
The green charging section on the dials doesn't show anything.
I can upload some proper photos when I have a low charge next but here is a photo showing where you adjust the hybrid mode battery reserve.
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