The iPhone 6s and iPhone 6s Plus will have reduced battery capacities compared to the current iPhones, according to reports.
Chinese tech site cnBeta says the iPhone 6s will feature a 1715 mAh battery and the 6s Plus a 2750 mAh battery - a decrease of 5.3 per cent and 5.5 per cent capacity respectively from the current models' 1810 mAh and 2910 mAh.
Apple 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.
British technology company Intelligent Energy recently claimed to have developed an iPhone that can go a week without recharging, running instead off a built-in hydrogen fuel cell.
The company has made a working iPhone 6 prototype containing both a rechargeable battery and its own patented technology, which creates electricity by combining hydrogen and oxygen, producing only small amounts of water and heat as waste.
The iPhone 6s and 6s Plus are likely to benefit from a new 12MP camera, capable of shooting 4K video, with the front camera capable of recording 1080p video at 60fps, 240fps in slow motion mode and flash support.
The new phones are also expected to sport Force Touch technology, which detects how hard the user is pressing and allows different actions to be carried out accordingly. According to reports, the technology will allow menu "shortcuts" that enable users to find options on menus more quickly.
One of the most prevalent rumours is that the new generation of iPhones will see the introduction of a new rose-gold model.
Apple has sent out media invitations for a press event on Wednesday September 9, where chief executive Tim Cook is largely expected to introduce a revamped Apple TV box set alongside the new phones.
The new box is expected to feature a touch-pad remote, extra inbuilt storage and Siri voice control for browsing and selecting programmes and films to watch, in light of a recent patent filing.
The new box is expected to run a TV-optimised version of iOS 9 with a refreshed interface and, for the first time, may be opened up to the app community, with Apple expected to unveil a software development kit (SDK) that allows developers to build apps.
At present, only a handful of third-party programs feature on the Apple TV and introducing an SDK and App Store would expand this significantly.
It will also support Homekit, after Apple confirmed that Apple TV would act as a central hub for its connected home appliances, including ecobee thermostats, lighting kits and smart sensors.