It has a 15W CPU in it, it's not a screamer. It's not hard to have extremely long battery life in a laptop, just toss an extremely low power (15W or less) CPU in it and get the battery as close as you can to the somewhat arbitrary 100Whr limit that isn't really a limit but no one will sell a laptop you can't take in the cabin of an airplane.

What is hard however, is getting long life out of a performance laptop with a 45-60W CPU when you're capped to a 100Whr battery.