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Have Intel’s new Haswell processors really stretched battery life?

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Intel always makes two claims when launching a new line of mobile processors: better performance, and better battery life. Traditionally, performance has taken precedence over battery life, but the company’s message was different with Haswell. We were promised the best improvement in battery life ever delivered by a new architecture, with some systems seeing up to 50 percent better endurance.

Claims are only that, however, and are often optimistic. Now that we’ve reviewed a handful of Haswell-powered systems, with both dual-core and quad-core processors, we’re going to take a closer look at just how much the new 4th-gen parts outpace their predecessors. Has Intel delivered, or was it all just marketing hype?

Apples to apples

Though we’ve now had a solid array of Haswell laptops to test, there is one particular systems that stands out as a great benchmark: Acer’s Aspire M5 Touch. What makes the M5 a benchmark is its consistency. Processor aside, the updated model we received for review with a 4th-gen Core i5 processor is almost identical to the older version with a 3rd-gen Core inside.

So, what did Intel’s latest and greatest do for endurance? Take a look at this handy graph.

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As a reminder, we use three tests to judge battery life. The first test is the Battery Eater test, which is a load benchmark designed to eat through battery life quickly. The second test is Peacekeeper, which is a Web browsing benchmark. And the third test we do is the Reader’s Test, which is a near-idle test that opens and scrolls through a text document.

Now, with these benchmarks in mind, the graph above shows some interesting results. In our Battery Eater load we see that the new Haswell-powered M5 actually goes flat more quickly than the older Ivy Bridge laptop. The situation reverses in Peacekeeper, however, where the new M5 has a 40-minute advantage. And when we look at the Reader’s Test, we see the gap grow to over 3.5 hours.

Clearly, the new model has better battery life overall, but not in every situation. Is this true of other Haswell laptops?

Big gains for near-idle use 

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Above are the Reader’s Test battery life results for all five laptops we’ve reviewed with a 4th-gen processors. These results are, in a word, outstanding. Even the Asus G750 and Razer Blade managed to last over five hours, which is incredible for quad-core systems boasting discrete graphics. Similar systems with 3rd-gen processors usually struggle to offer four hours in this test, and some don’t even last three.

The graph above absolutely supports Intel’s claim of an up to 50 percent increase in battery life, and even that claim actually looks conservative in light of these figures. The Asus G750, for example, has nearly tripled its endurance relative to the preceding Asus G75V. That system lasted just two hours and 18 minutes in the Reader’s Test.

Web browsing is impressive, too

While the results look impressive, you might be wondering if it matches real-world results. This is a good question. Our Reader’s Test is not at all demanding, so what happens when Haswell laptops are put under a moderate load?

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The results from Peacekeeper, a Web browsing benchmark that we loop until the battery gives out, tells two interesting stories. First, all systems display lower endurance than they did in the Reader’s Test; and second, laptops with a dual-core processor suffer far more than those with a quad.

Let’s deal with the second point first, as it’s more mysterious. One might expect a quad-core to suffer the larger hit, but that assumes all cores will be active. Peacekeeper is a browser benchmark, so it’s not heavily multi-threaded. A substantial portion of a quad-core chip’s potential performance remains at idle, and those cores that are used often operate at a lower clock speed then those found in a dual-core processor. These factors combine to soften the blow to battery life. We’ve seen a similar effect with previous quad-core laptops, and Haswell doesn’t change the story.

The dual-cores muster a larger portion of their potential, and battery life spirals downward as a result. The Sony Vaio Pro 13 did not outlast the Razer Blade in this test, and the Acer Aspire M5 sees its endurance nearly cut in half. Yet, even so, the results do show a notable improvement. While an average 3rd-gen laptop could deliver 3.5 to four hours of life, Haswell systems seem to be heading towards an average of about five hours. That’s nothing to laugh at.

No improvement at load

Last, but far from least, we must examine Battery Eater. This load test is designed to consume battery quickly, resulting in an example of how long a laptop will last under worst-case conditions. How’d Haswell do?

haswellbatterylife4On the whole, Intel’s latest and greatest hasn’t moved the needle. All of the systems came in around two hours, which is about the average for laptops with 3rd-generation Core processors.

The lack of improvement here may seem unusual, but it’s actually not a huge surprise. The enhancements made to Haswell, which extend maximum endurance, can’t overcome the fact that high processor load directly translates to high power draw. Our wattmeter has indicated that the 3rd-gen and 4th-gen systems consume about the same amount of power at load, so we’d expect to see similar endurance at load.

While this might seem a disappointment, we don’t think Intel can be faulted. Squeezing greater efficiency from current hardware is not easy, and no one is doing a better job. The reality is that we’ve passed the point in processor technology where big gains are “easy” to realize. Moore’s Law is not dead, but expotential growth in transistor count no longer offers similar gains in performance and efficiency.

Breaking down the results

The Haswell laptops we’ve reviewed thus far offer a clear verdict. Battery life has improved overall, but results will vary.

Both the near-idle Reader’s Test and Web browsing Peacekeeper benchmark show battery life consistent with Intel’s claim of an up to 50 percent improvement compared to 3rd-gen processors. In fact, the near-idle test makes that look like a conservative number, as Acer’s Aspire M5 improved by just over 65 percent. If you’ve been holding off on buying an Ultrabook because you’d like better battery life, the new 4th-gen Core lineup may be what you were waiting for.

With that said, life at load hasn’t changed at all. Haswell is great for mobility, but it’s no miracle. Heavy workloads will still cut through a battery like butter.

Intel deserves credit for what it has accomplished, as this is almost certainly the largest generation-over-generation improvement in laptop battery life ever achieved. Yet, at the same time, these results hint at the limitations of the world’s most powerful consumer CPU. These numbers still depict a product that’s much better suited for laptops than tablets or 2-in-1s; we may have to wait until the new Atom architecture debuts later this year to see significant progress from Intel on that front.

Image credit: Thomas Hawk/Flickr

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Matthew S. Smith
Matthew S. Smith is the former Lead Editor, Reviews at Digital Trends. He previously guided the Products Team, which dives…
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