The ThinkPad X1 Carbon includes a 57 Wh battery, which is around the mark of most other 13-inch laptops. Of course the X1 Carbon includes a 14-inch display, though this should make only a minor difference to battery life. Improvements to the efficiency of Kaby Lake also play a part here.
Across our suite of battery benchmarks, the ThinkPad X1 Carbon performs extremely well. Topping the charts in our Wi-Fi test is a particularly impressive feat, and illustrates just how well suited this laptop is to typical work use cases. 7 hours of life in the Wi-Fi browsing benchmark equates to well over 10 hours of normal use, which is a fantastic result.
Lenovo does state the X1 Carbon is good for 15.5 hours of life, though I suspect this is only possible with low brightness and less intensive use cases.