Tech news site cnBeta says the battery capacity of the standard-sized new iPhone will be reduced from 1810 milliampere hours to 1715 mAh, and the large-screened model will drop from 2910 to 2750 mAh. That amounts to a power drop of 5.3 per cent for the iPhone 6S or 7, and of 5.5 per cent for the larger iPhone 6S Plus or 7 Plus.
"These aren’t huge decreases," says Forbes, "but it is of particular concern for the iPhone 6S as battery life is already one of the worst features of the iPhone 6."
iPhone users frequently complain about their handsets being unable to make it through the day without needing to be recharged.
Many had been hoping that the iPhone 6S or 7 would herald an improvement in battery life, particularly because Apple appears to have been focusing on the problem.
The company "has made a point of how new operating system iOS 9 will be more energy efficient than iOS 8, including a new Low Power mode and new updates adding around an hour to battery life," says the Daily Telegraph.
Software improvements may compensate for the new iPhones smaller batteries, but it seems clear that prospective customers should not expect a significant increase in battery life.
Apple is expected to unveil the iPhone 6S or 7 at an event in California on 9 September. It never comments on new products in advance of their official launch.