By JP Mangalindan
June 18, 2013

FORTUNE — With laptops, all-day battery life remains an elusive, almost mythic, thing. Because unless it’s an HP (HPQ) laptop with a protruding 12-cell battery, reaching anywhere north of seven hours of use between charges is near-impossible.

But the new MacBook Air models, announced at WWDC, are supposed to be exceptions: Apple (AAPL) rates the 13-inch model at 12 hours of battery life and the 11-incher at nine. That’s four-plus hours more than before — a potentially serious improvement. To suss out the claim, Apple loaned us an 11-inch unit stocked with a 1.3GHz dual-core i5 processor, 4 GB of RAM, and 256 GB of flash storage, a model that sells for $1,199.

Little has changed on the outside. For newcomers, that should be just fine, since — let’s face it — the Air’s clean lines and 2.38 lb. waif-like frame are still nice to look at, even three years later. Inside, Apple has made small tweaks. There are now two microphones instead of one, and the flash-based storage is supposedly 45% faster. The biggest change in this otherwise minor hardware upgrade is the inclusion of one of Intel’s (INTC) fourth-generation Haswell processors.

With Haswell, Intel promises better energy savings and a serious graphics bump without trading performance. The Air has an ultra-low-power version of the chip, ranging from a 1.3 GHz dual-core i5 to an optional 1.7 GHz dual-core i7, called “ULT.” Apple says the battery sizes in this year’s models haven’t changed. It’s the new processor and its improved power-conserving ways that are responsible for better battery life.

MORE: Apple’s new Mac: What is this thing?

Over the course of a week, the 11-inch Air ran much longer before it needed to be plugged in. While the old Air might run three hours before shutting down, this year’s power-sipping model averaged around 5.5 hours under a mix of conditions, like streaming Spotify, watching a 22-minute episode of Arrested Development from Netflix Instant (NFLX), and browsing the web with Wi-Fi on and brightness dialed up. Separately, when we kept things simple — browsing the web with Safari, writing in Google (GOOG) Docs, brightness dimmed to 3/4 — the Air managed an impressive 8.5 hours.

Opening apps, toggling through windows, and watching high-definition video is a smoother experience than before, but the small speed bump isn’t one many will notice. As for Intel’s claim that Haswell offers better graphics performance? The first-person puzzle game Portal 2 was solid with some of the graphics bells and whistles turned on, but much less so when we tried everything on full throttle. In other words, expect more contemporary games to be playable, provided those settings are kept medium.

A week with the new 11-inch MacBook Air has convinced me that Apple’s hardware upgrade — minor as it may seem — will still be enough to convince some to upgrade or buy one for the first time based on excellent battery life alone. It doesn’t achieve nine hours between charges with everyday use, but 8.5 hours of web browsing is pretty close. And while I wish Apple would offer a build-to-order option for a higher-resolution screen — the current 1,366 x 768 resolution is really starting to feel cramped — it’s a small omission on an otherwise excellent device. The ultimate road warrior’s notebook? For just over a grand, it’s hard to argue otherwise.

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