Is iOS4, iPhone's new OS, a Battery Hog?
Multi-tasking apps tax the iPhone's battery, so Apple has sought to institute power-saving tricks elsewhere. But they won't do you any good if you don't take advantage of them.
Tue, July 27, 2010
Since most people don't have a new iPhone 4, which comes with a bigger battery, most iOS 4 users are running it on an iPhone 3GS or 3G. This means you're probably experiencing less battery life if you upgraded operating systems to iOS 4.
Keep in mind that an iPhone's main battery drain comes from the 3G radio and broadband chip, LCD screen, CPU cycles and, to a lesser extent, main memory (also called Mobile DDR). The battery drain stems from iOS 4's multi-tasking feature and how it taxes main memory and the CPU.
Here's the problem: Background apps are loaded into main memory where they're restricted to a couple of APIs for background processing. "It's not drawing a ton of power, but system memory has to be refreshed by the CPU constantly," which means background apps tap the battery, Vronko explains.
How much battery drain? Vronko says the multi-tasking feature means that most of the 256MB of Mobile DDR in an iPhone 3GS on iOS 4 will be occupied. Thus multi-tasking can consume up to 10 percent of the total charge over the course of eight hours.
Compare this with the iOS 3, where only a few proprietary Apple (AAPL) apps ran in the background. For most iPhones, a portion of the 256MB of Mobile DDR wasn't being used (not withstanding a big game app running in the foreground requiring, say, 200MB of memory). This means that memory was consuming only 5 or 6 percent of the total charge over eight hours.
"With only one main application running, memory usage would have been low enough that the OS could have frequently turned off a quarter or even half of the memory, saving critical power," says Vronko. Given iOS 4's use of memory, iOS 4 probably drains 10 to 15 minutes more than iOS 3 per charge, he says.
Multi-tasking apps also require extra processing. While the small number of APIs and processor time available to apps running in the background minimizes the increase in processor load, "it can't prevent it completely," Vronko says. "I expect that the battery impact from Apple's frugal flavor of multi-tasking is probably still 4 to 5 percent. While that's probably significantly less than the hit taken on a more open platform like Android, it will probably still account for another 10 to 15 minutes per charge."