I drive an electric car. I was giving a friend a ride one day and offered him a USB port to charge his phone, since he was low on battery, but he was reluctant

I drive an electric car. I was giving a friend a ride one day and offered him a USB port to charge his phone, since he was low on battery, but he was reluctant because he didn't want to waste my car's battery. We did some quick mental math and figured that charging his phone from empty to full would take about as much energy as driving the car a few inches. He plugged the phone in.