“A small number of customers have reported lower than expected battery life on iOS 5 devices,” Apple said in a statement to AllThingsD. “We have found a few bugs that are affecting battery life and we will release a software update to address those in a few weeks.”

Sam Radford on the mysteriously shorter battery life of the iPhone 4S, and how to improve it: "one suggestion: a full restore of the iPhone. This meant plugging my phone into iTunes, choosing the ‘Restore’ option, waiting for the operating system to download afresh from Apple, installing that, and then restoring my iPhone from my backup.

"And you know what? It did make a difference… But, to be clear, it was still not on a par with what I was getting with the iPhone 4.

"I kept my eye on Twitter for any other suggestions being shared and one popped up which talked about ‘calibrating’ the battery. This basically means charging the battery to 100% and then letting it completely drain to nothing before charging it again.

"I did this yesterday and this too has definitely led to another noticeable boost in battery life. And whilst my iPhone 4S is probably still not quite as good as the iPhone 4, I do think it is now pretty close."

Is the A5 processor to blame?