The battery life of the Apple Watch may last through about 2.5 hours of heavy use, 3.5 hours of standard app use, and between two and three days of standby or low-power use.

So says a news report today, citing sources close to the development of the Apple Watch.

Previously the only information we had on this was a statement by Apple chief Tim Cook that Watch users would need to charge the device every day.

Mark Gurman of 9to5Mac cited “people with knowledge of the Apple Watch’s development” for information on the specific performance targets Apple wants to hit for the Apple Watch battery. The actual numbers may fall short of those targets, he added.

Gurman’s sources said that Apple decided to use a powerful processor and a high quality screen in the Watch, both of which can soak up a lot of battery power. The processor will be close, performance-wise, to that of the A5 battery used in the current generation of iPod Touch, the report claimed. And the Retina-class display can update at 60 frames per second. The Watch will run a stripped-down version of iOS called “SkiHill,” Gurman wrote.

Apple, the report says, has been concerned over the past year about the battery life of the watch. That factor alone was enough to push the retail launch of the device from the originally planned late 2014 date into 2015.

Apple has been trying to match Watch’s battery size and life with the ways users will use the device. The company has now decided that users will want to be able to actively interact with the Watch for 2.5 hours of processor-intensive activity, like game play, or for 3.5 hours of standard app usage.

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