How did Apple make the iPhone's battery last longer?

Answers to your questions about the news.
June 22 2007 5:36 PM

Where'd Apple Get Its Juice?

How they made the iPhone battery last longer.

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The Apple iPhone. Click image to expand.
The Apple iPhone

Apple 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?

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.

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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 thephone'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 screenwhen 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.

David Sessions is a former Slate intern. He is currently a blogger at Politics Daily.

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