Apple has unveiled its own Smart Battery Case that slides onto the back of the iPhone 6 or 6s to provide additional power.
According to the tech giant, the silicone case offers up to 25 hours of talk time, up to 20 hours of high-definition video playback and up to 18 hours of web browsing.
The £79 accessory is available in white and grey and resembles a standard phone case, except for a protruding rectangular bump on the back.
A cut-out section allows owners to use their camera, and the case includes an acoustic port that channels audio from the phone's speaker. Apple said the case's in-built antenna ensures the accessory doesn't interfere with phone signal.
The interior of the case is lined with microfibre that offers additional protection for the device inside, and also cleans the back of the phone when the case is slid over it.
Using the swipe-down notifications centre, users can check battery levels for the case at the same time as the phone, and can charge both devices at the same time.
The case has drawn some criticism in the press, with the Guardian likening the design to a "cheap Chinese knockoff", and Wired describing it as "so ugly it's almost sarcastic".
Apple launched the iPhone 6 in September 2014, although rumours of it accidentally bending in owners' pockets quickly followed.
The company updated the phone earlier this year with new 3D Touch sensor technology, which responds to pressure as well as tapping and swiping gestures, and a more robust case.
In addition to new versions of the iPhone, the company this year released the Apple Pencil – a stylus designed for technical drawing that responds to different pressures and angles.
Apple is also rumoured to be working on a touchscreen smart ring, and its first electric car.