An update to iOS 5 is the works, says the computing giant, adding that it is already testing the new version with developers.
Whilst the bulk of battery problems have come from users of the iPhone 4 and 4S series, some users of the iPhone 3GS have also reported that their batteries have been running down in just a few hours.
On this writer's iPhone 3GS, when running a specific app at the weekend, the battery appeared to run down overnight, despite a full charge, and the story is the same on many Apple forums.
Apple's statement on the issue: "A small number of customers have reported lower than expected battery life on iOS 5 devices. 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."
The Guardian newspaper, meanwhile, quotes one iPhone user as saying that she has been getting around 10 to 12 hours with the phone on standby, but the battery indicator drops by 1% every minute whilst browsing the web.
The Apple Insider says that Apple has released an initial beta iOS 5.0.1 build 9a402 to developers to begin testing the new update on iPhone, iPod touch and iPad.
The new build, says the newswire, fixes bugs affecting battery life, as well as adding multitasking for the original iPad, and resolves bugs with documents in the cloud. As well as security improvements, iOS 5.0.1 beta is also said to introduce a new way for developers to specify files that should remain on device, even in low storage situations.