Good morning.

three weeks into owning my iv, last night for the first time I kept the setting as full hybrid.

 

I noticed that even when the engine was running, the range on the electric was decreasing (whilst on the motorway)

 

so does the battery also get used whilst the engine is running (the rev counter was showing so I know the engine was running, although I also see when it goes back to electric)

 

Hope that makes sense 

Indeed, while in hybrid mode, even when the ICE is running there's some use of the HV battery - it will sometimes give some electric support for the acceleration. That happens when you keep the default settings of the hybrid drive. However, depending on your battery needs along the way, you can choose to preserve a certain amount of battery (or even charge while driving) for later use on your trip.

I advice to put instant consumption values on your VC and that will give you a good idea of what is happening there. In short, yest, battery is always consumed when accelerating and often when maintaining speed but not much power needed (like driving down the hill - car may decide to consume some 2-3kWh/100km instead of switching ICE on).