Why does the car use engine power even when it has battery charged

Hello, I would recommend you read over your vehicle's owner's guide to fully understand the operation and functionality of your new Volt. Additionally, consult your selling dealership with any questions related to vehicle operation. In brief, depending on conditions such as load, accessory usage, acceleration, speed, temperature, and battery state of charge and usable capacity, your engine may operate to supplement the power available with the hybrid battery. Also remember that the higher a speed you are driving and the quicker you attempt to accelerate, the more likely it is that your engine will assist for performance needs.