Buy For All Day Battery Life
The 2019 MacBook Air battery life is rated at 12 hours by Apple, and if you play movies locally in iTunes it is at 13 hours. That's with 75% brightness. Apple typically is pretty accurate with Mac battery life claims.
This specific battery test is with the 1.6GHz dual core MacBook Air with 8GB Ram and a 256GB SSD. You can expect similar battery life on other configurations as well.
With a USB C and a 30W charging cord, you can also carry around a USB C PD battery pack if you need to go longer than 12 hours without finding an outlet. This makes it a super portable device for the long haul.