If you need 100 kWh into the truck’s electric motor to drive somewhere, with a battery electric truck you need to generate around 120 kWh at the power station. After transmission losses, transformer losses, charging and discharging the battery, etc you wind up with your 100 kWh.
If you’re driving a hydrogen fuel cell vehicle, you still have an electric motor and you still need 100 kWh to reach your destination. But you need to generate something like 400 kWh to actually get 100 kWh into the motor, and that 400 kWh of generation and grid transmission is what you need to pay for. Turning electricity into hydrogen and back into electricity is incredibly wasteful.