Rumor: Apple to boost 4.7" 'iPhone 6' battery by 15% over iPhone 5s

"iPhone 6" and "iPhone 6c" concepts by Martin Hajek.

If true, the more diminutive device would receive a battery capacity bump significantly larger than the 8 percent jump between the iPhone 5 and the current-generation iPhone 5s, likely attributable to the increased power demands of the larger display. The report was first published by Chinese technology website IT168.

The stated 2,500 mAh capacity of the widely-rumored 5.5-inch "phablet" variant, meanwhile, would be an increase of 60 percent from the iPhone 5s. Despite the seemingly substantial increases, they would place Apple's offerings behind similarly-sized devices from rivals like Samsung and Motorola.

Samsung's flagship Galaxy S5, for instance, sports a 2,800 mAh battery alongside a 5.1-inch display. Motorola's Moto X packs a 2,200 mAh battery with its own 4.7-inch screen.

One reason Apple might consider such a move would be as part of a strategy to slim down the next-generation devices, as larger-capacity batteries bring with them a corresponding increase in size — the Galaxy S5, despite a larger frame in which to place the battery, is still thicker than the iPhone 5s. The Cupertino company could also have designed a much more power-efficient architecture, thanks to their impressive vertical integration, that would allow runtime to remain the same despite the lessened power reserve.