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Where'd Apple Get Its Juice?How they made the iPhone battery last longer.

By David SessionsUpdated Friday, June 22, 2007, at 5:36 PM ET

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The Apple iPhoneApple announced on Monday that its much-anticipated iPhone will offer eight hours of talk time rather than the previously announced five. On Wednesday, Jack Shafer mocked journalists for lavishing attention on this tiny morsel of news. Even so, that clever bit of Apple PR got Explainer wondering: How do you make a battery last longer?

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Tweak the hardware. Cell phone batteries are often as large as the gadget's casing can accommodate, and there are no surprise technologies that can make a standard battery retain its juice longer. Instead, manufacturers concentrate on power management.

Related in Slate

Jack Shafer inaugurated the Apple Suck-Up Watch. Clive Thompson revealed why laptop batteries aren't evolving with the computers they come in. Timothy Noah heralded Dell's quiet recall of their combustible laptop batteries. Michael Agger predicted the future of stalking with the dawn of the camera phone. Daniel Gross wondered if everyone on earth needs a cell phone.

One way to improve power efficiency is to upgrade the hardware. A smart phone's circuit board incorporates dozens of chips that control the display, operating system, and the phone's wireless connection, among other things. Along with the screen, chips are the biggest power-consumers in a cellular device. By working with numerous chip manufacturers, Apple and other electronics companies can pick and choose individual chips that are particularly energy efficient. The iPhone's glass screen, announced this week, will also help save energy. Glass transmits light more efficiently than plastic, which will allow the iPhone's screen to maintain the same brightness while using a little less power.

Another way to extend battery life is to shut down parts that aren't in use. The more tasks a phone is running (phone calls, Web browsing sessions) the more quickly the battery gets depleted. Advanced operating systems—iPhone uses a version of Apple's OS X—can regulate the device's power usage, powering down the processor or the screen when they're not active. (Tech companies occasionally calculate a device's battery life with most of its hardware components shut off, an unrealistic situation that tends to produce an inflated projection of the gadget's real-world power consumption. Apple claims it tested iPhone's talk time with all of its default features turned on except the Wi-Fi network scanner.)

Most consumer electronics, including the iPhone, are powered by lithium-ion batteries. These power sources are popular because they pack many times the power of other types of batteries in a fraction of the space. Still, chemists can't do much to change the amount of electrical current created by the chemical reactions inside a lithium-ion battery. The only way to build a more powerful battery is to make it larger, thus creating space for extra chemicals.

Bonus Explainer: Since batteries aren't getting better and phones keep adding features, how are next-gen devices going to have enough juice? Tech analysts say new screen technology will offer a huge amount of power savings. A large touch screen like the one on the iPhone is particularly power-intensive. As a result, gadget manufacturers are increasingly ditching traditional LCD displays in favor of the more energy efficient organic light-emitting diode screens. OLED screens are more expensive to produce than their LCD counterparts, but they put out virtually the same amount of light as a conventional screen while using a fraction of the energy.

Got a question about today's news? Ask the Explainer.

Explainer thanks Richard Doherty of the Envisioneering Group, Rob Enderle of the Enderle Group, Ian Hill of the NRC Institute for Chemical Progress and Environmental Technology, and Brian Lam of Gizmodo.

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David Sessions is a former Slate intern. He is currently the editor of Patrol.

Photograph of Apple iPhone courtesy Apple.

COMMENTS

Remarks from the Fray:

If you use your cell phone while travelling in your car, get a rooftop antenna & your battery life will show a significant improvement.

Most cell phones adjust the transmitter power to the minimum level necessary to maintain a good connection with the nearest cell tower. In fringe areas, the nearest tower might be some distance away, so your cell phone will find it necessary to crank out the full 300 milliwatts it's capable of producing.

The weak link is your cell phone's antenna. Newer phones all have internal antennas, the kind that don't protrude from the top of the case. They're very sleek, and they don't break off when riding around in your pocket, but they're not very efficient when it comes to converting transmitter power into an effective radiated signal. If you're inside your car, the metal automobile body also sucks away some of your signal, making it very difficult for your cell phone to transmit data to the cell tower. To compensate for all these inefficiencies, your phone has to run at maximum power to stay connected. Battery life is very short in rural areas.

The way to fight back is to get an external antenna and mount it in the middle of your car's roof. The antenna itself, when compared to the hidden antenna in your phone, is at least ten times more efficient than your phone's built-in antenna. Plus, it's outside the car, so it doesn't suffer the energy loss involved when the signal passes through the sheet metal of the car's body. Finally, mounting the antenna in the middle of the roof creates something called a "ground plane," which dramatically improves the radiation pattern of the antenna.

The end result is that a roof-top antenna is probably 100 times more efficient than your cell phone's internal antenna when used from inside the car. This means your phone can lower its transmitter power and still stay connected to rural cell towers, cutting way back on battery drain. Another bonus is that you'll be able to talk in places that were formerly "dead zones" because the external antenna allows you to connect with cell towers at a greater distance than with an internal antenna.

--Arlington

(To reply, click here.)

You missed a critical part of making cell phone batteries last longer. Sure shutting down unnecessary parts of the device is a large part. But one of the largest parts of power drain in a cell phone is the radio. Modern radios in cell phones periodically query (connect to) the nearest cell-phone sites to self-identify and to figure out what the proper power setting should be if a connection (call) is initiated.

The frequency of this interaction, the logic behind what level of power it is conducted at all go into dramatically impacting the power drain of the phone.

so a good way to improve battery life is to tweak and tune and tweak both the voice and data connections. And since the iPhone is heavy on the data connections, my suspicion is that Apple spent a lot of time figuring out how to deal with internet applications and websites that periodically exchange 'keep-alive' messages. And in doing so have dramatically improved battery life by using less of it.

--degsme

(To reply, click here.)

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