Following its release last year, there were various reports of the iPhone 4S - an upgrade to 2010's iPhone 4 - rapidly draining its battery life, even with just light usage.
Apple addressed the issue with an update to its iOS 5 operating system, after finding that the problem was down to flaws in the software, although some users still reported issues after the patch.
Many smartphones users buy backup batteries for their devices, just in case they run out of battery life while on the move, although this means carrying around an extra item.
Danish tech firm Sandberg has now come up with a solution in its BatteryCase product, a hard-back case for the iPhone 4 that is claimed to double the phone's battery life.
The BatteryCase can be charged from a computer or with the iPhone power adapter, before being connected to the iPhone to increase the battery time.
"It's not enough to just create things that work. People have obviously chosen to use a mobile because they want to be mobile," said Martin Hollerup, the managing director of Sandberg's BatteryCase division.
"The more additional devices we can avoid and the more cables we can leave at home, the better we experience being mobile. The BatteryCase provides you with plenty of power for music, video, Wi-Fi, and so on. This means an end to worrying about when you can next recharge."
The Sandberg BatteryCase is said to be "already on its way" to stores, priced at £32.99. The product is covered by a five-year warranty.