Apple has admitted that "a few bugs" in its latest mobile operating system iOS 5 are affecting the battery life of some of its devices. It said that it will release a fix in the next few weeks. The issue came to light over recent weeks with thousands complaining on Apple's forums about poor battery life. In some cases, people claimed that their phone battery was draining by up to 15% every hour, even when the handset was not being used. The issue was not limited to Apple's new iPhone 4S handset but also affected some of the firm's iPad tablet computers which had installed the upgrade. Initially Apple would not comment on the matter but late last night it issued a statement: "A small number of customers have reported lower than expected battery life on iOS 5 devices," it said. "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," it added. Global sales When the iPhone 4S was announced last month, some were disappointed that it offered no radical changes. Despite that sales have been huge, with Apple claiming to have sold over four million handsets in the first three days. Apple's servers were also overwhelmed by demand for iOS 5 when that was released. Globally though Apple is beginning to feel the heat of rivals, especially from vendors using Google's Android operating system. Research firm Strategy Analytics found that in the third quarter of this year Samsung overtook Apple with 27.8m smartphone shipped compared to 17.1m iPhones. And this week, analyst firm Canalys revealed that HTC has become the number one vendor in the US, overtaking Samsung, and pushing Apple into third place. Tim Coulling, an analyst with the firm, said the latest issue should not affect sales. "It is not as bad as the antenna issue that affected the iPhone 4. This is about software and Apple can push out updates very quickly," he said.