Online

Apple MacBook Air: apple.com/macbook-air

Dell XPS 12: dell.com/us/p/xps-12-9q33/pd

Sony Vaio Pro: bit.ly/1f314rE

Acer Aspire S7: acer.com/aspires7

NEW YORK — Just in time for the back-to-school season, new laptops with extended battery life are hitting store shelves.

What these laptops have in common are microprocessors from a new family of Intel chips called Haswell. The chips consume less power than previous generations and promise a 50 percent boost in battery life for watching video. The improvements extend to word processing, Web surfing and other computing tasks as well.

Put another way, you can unplug your laptop in the morning and go a full day without a charge, with some breaks for meals, exercise and errands.

The catch: Slim, lightweight laptops with Haswell chips cost more than $1,000. Cheaper laptops will be heavier or come with older chips.

I reviewed Apple’s MacBook Air and Dell, Sony and Acer computers running Microsoft’s Windows 8. Samsung and other PC makers are just coming out with Haswell laptops, so you should expect even more choices by the holidays. The four I tested use solid-state flash drives, which keep laptops light but don’t have as much capacity as traditional storage. They also lack ethernet ports for wired Internet connections and slots for DVDs. Expect to use Wi-Fi a lot, though USB ports are available to connect devices. Base models come with 128 gigabytes of storage. You can spend a few hundred dollars more for additional storage and faster processors.

Here are the four Haswell laptops I tried, starting with the cheapest:

MacBook Air from Apple. Starts at $1,099, 13-inch model.

With a screen measuring 13.3 inches diagonally, the larger model weighs 2.96 pounds and costs $1,099. An even lighter, 11.6-inch version is available for $999, but promised battery life is just nine hours. Spend the extra $100 for three additional hours and a larger screen if you can afford it.

Although promised battery life on the 13-inch review unit was 12 hours, I was able to get more than 14 hours once by turning off the Wi-Fi connection. I typically got nine to 11 hours for general Web surfing. Apple promises up to 10 hours for playing video downloaded from its iTunes store. I ran that test four times and got nine to 10 hours of playing the same episode of “Revenge” over and over. As with other laptops, performance drops significantly when streaming video over Wi-Fi, down to six to seven hours of Hulu.

XPS 12 from Dell. Starts at $1,200.

The XPS 12 is part of a category called ultrabooks — slim and light laptops. They run Windows. It’s also a convertible. In one position, you get a laptop. Spin it 180 degrees, close the lid, and you have yourself a tablet. Magic.

Unfortunately, the XPS 12 is on the heavy side. The base model is 3.35 pounds. It’s less than a half-pound heavier than the Air, but in practice, it feels heavy, especially as a tablet, at more than double the 1.44 pounds for the full-size iPad.

Promised battery life is about 8.75 hours. I got nearly 8.5 hours for word processing, spread- sheets and other tasks that didn’t need Wi-Fi. With wireless turned on, I got 7.5 to eight hours of use. Like the other two Windows machines, I got five to six hours of iTunes video. That’s about half of what I got on the Air, but Apple has the advantage in being able to optimize its hardware for the software it designs. I got 5.5 to six hours of streaming video on Hulu, which is just about an hour less than what I got on the Air.

I did have some trouble with the battery losing its charge quickly when not in use, but a software update seems to have fixed that. That said, the XPS 12 took up to four hours to get a full charge, compared with two hours or less for the others.

Vaio Pro 13 from Sony. Starts at $1,250.

The Pro is an ultrabook that’s very light. The 13.3-inch laptop weighs just 2.34 pounds. Sony uses carbon fiber to keep it light. It feels to me like cheap plastic that’s about to break because it bends. But Sony assures that it’s more durable than aluminum. And it says the fact that it bends isn’t a sign of weakness but a characteristic that lets it absorb shock. You can save $100 with an 11.6-inch Vaio Pro 11 instead.

I consistently got more than the seven hours of battery life promised for general Web surfing and word processing. I reached 8.5 hours once with Wi-Fi turned off. Battery life drops below six hours, though, for iTunes video download and Hulu streaming. If you do a lot of that, you can add a spare battery for $150, doubling the battery life. The system is still less than 3 pounds with the spare battery attached. The other units I tried won’t let you replace batteries or insert a spare.

Aspire S7 from Acer. Starts at $1,450.

The Aspire has what I want in a laptop, except for the price. The aluminum body is covered on one side with glossy white glass. I came to appreciate the durability it brings once I started lugging it around. It’s also fairly light, at 2.87 pounds.

You can flip its screen all the way back so that both the keyboard and the screen are level with the surface, just like a tablet on a tabletop. Acer says it’s good for presentations. Press Function-O on the keyboard and the image on the screen rotates 90 degrees at a time, allowing you to show something to others at your table.

Acer’s website promises eight hours of battery life. I exceeded nine hours with Wi-Fi off and got seven to 8.5 hours of Web surfing. But I got less than six hours of iTunes video and Hulu streaming.