It consumes a lot less energy than you’d expect. They also have something called “cabin overheat protection” which basically kicks on the AC throughout the day to keep the interior from going above 100 degrees which happens easily in any car left in the sun in the summer. With a full glass roof and full black interior it’s particularly useful and helps keep the dash and seats and everything from excessive wear and warping.
Last week we were in the high 90s and even hit 100, and with the cabin overheat turned on, the car only consumed about 9 miles of range in 8 hours in the middle of the day. The electric equivalent to gas mileage is called MPGe and is a handy way to proxy what an electric car would get if it ran on gas, and my Tesla is rated at 130mpge which means it only used about 6% of 1 gallon of gas to keep the cabin cool all day long. Using full dog mode to keep the cabin at 72 degrees seems to run about double, maybe a little more energy consumption, but even still you’re looking at a fraction of a gallon of gas equivalent. In more direct terms, it’s cost me roughly $0.02/mile of range in electricity to run my car for 4,500 miles, so leaving the AC on for 8 hours in the middle of the day would cost less than a dollar (and not be polluting all day long like an ICE car). Honestly an electric truck/SUV will be just about the greatest thing to happen to car camping/sleeping in the back since you can keep hvac on all night silently and without creating a toxic and dangerous environment in the process.