The new MacBook Air 15.3 inches is 21% bigger and the screen area where there's about 21% more of it. For those extra that extra bits that you get exactly the same rated battery life according to Apple. The other thing that they did with the extra space provided to them is they put more speakers. This is the first time they've had a 15 inch laptop that doesn't have speaker grill holes on the side. It really does feel like you're just using the same computer, but bigger.