Apple has released a battery case,, called the Smart Battery Case, that improves the iPhone's battery life by up to 25 hours.
Third party vendors, such as Mophie, already produce various battery cases that plug into the iPhone's Lightning port and provide extra power beyond the built-in battery.
The case comes in black and white versions and is designed for the iPhone 6 and 6S.
Apple claims that simultaneously charging the Smart Battery Case and iPhone yields over 25 hours of talk time, 18 hours of internet usage, and over 20 hours of video playback.
The case costs $99 (£66) in the US but does not appear to be available in the U.K.