The older ThinkPad X1 Carbon 2014, with its 46-watt-hour battery, does the worst at 431 minutes. I'm expecting to see the updated ThinkPad X1 Carbon soon, so we'll see whether the X1 Carbon can stage a comeback.
There's nothing budget about the specs
Moving back to the physical attributes of the ZenBook, I have to say I expected far more corners to be cut. For example, I expected the 13.3-inch screen to be an inferior TN panel. Instead, Asus uses a 1920x1200 resolution IPS screen and an anti-reflective coating. Asus makes a version with a 3200x1800 panel and also offers optional touch. The 1920x1200 display is competent. I didn't see any terrible color banding, and although Asus rates it at 300 nits in brightness, it pegged our meter at 340. I did see noticeable light leakage from the backlighting when cranked up to maximum in a dark room. But at normal brightness levels for a darkened room, it's not atrocious.
In storage, I also expected a budget move too, like a hybrid drive or a leftover mSATA drive. Nope. Asus actually surprises with a 256GB M.2 SATA SSD. Let me say that again: A 256GB SSD. If you think about it, that's far more than what you're getting anywhere else. Period.
The keyboard isn't bad either
I even found the keyboard to be pretty good. One of my complaints with Dell's XPS 13 2015 model is a slightly compressed keyboard and small keys. Its keys measure 14.7mm wide and tall. The ZenBook's are 16.2mm wide and 14.7mm tall. That may sound like nothing, but my typing was more accurate on the ZenBook's even though the keys felt a little spongy to my digits. If I were nitpicking, I'd note the lack of backlighting — and then Asus would just throw the $699 price in my face and tell me where to go.
The trackpad on the unit appears to be an Asus design. My reference is the Google Chromebook Pixel's excellent etched-glass trackpad. This is not in the Pixel's class and has a definite metallic feel, but it's quite usable, and palm rejection on the default settings was quite good.
If you were looking for something to complain about, it would be the wireless. Asus put in a dual-band 802.11n radio instead of 802.11ac. For most people it won't matter and is probably worth the trade-off for the extra RAM and storage.
Conclusion: The best deal in town
What this comes down to is a major breakthrough in price for an ultrabook. I thought Dell's XPS 13 2015, with its $799 price was a big breakthrough (and it is), but you give up in RAM and storage to get to $800. The same goes with Apple's MacBook Air 11, which has a tiny, low-res screen and, like the Dell, a limited 128GB of storage and 4GB of RAM.
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