The Kia Sportage Hybrid can use solely electric power, the engine by itself or a combination of the petrol engine and electric motor, depending on the battery's state of charge, the drive mode and the accelerator input. A car that uses a combustion engine to charge the battery alone and not drive the wheels is a range extender, not a hybrid. You can read our review of the Kia Sportage Hybrid here - www.honestjohn.co.uk/kia/sportage/road-test, and we also found that greater acceleration demands resulted in the engine revving quite hard, so we would expect this is a characteristic of the vehicle rather than a fault.