Users took to message boards on Apple's website to complain that the software remedy delivered Thursday hasn't corrected the flaw. The criticisms first surfaced after Apple released the mobile operating system last month, in conjunction with its new iPhone 4S. Apple said that it's looking into the matter.

"The recent iOS software update addressed many of the battery issues that some customers experienced on their iOS 5 devices," said Trudy Muller, a spokeswoman for Cupertino's Apple. "We continue to investigate a few remaining issues."

Apple also drew controversy last year over the previous iPhone's antenna, which would lose signal when gripped a certain way - a problem known as "Antennagate." Apple gave away free cases and updated the software to address those complaints. The iOS software runs on the iPhone, as well as the iPad and iPod Touch media player.

The company responded to the battery-life criticism last week, saying a "few bugs" have affected a "small number" of customers. Apple didn't elaborate on what was causing the problem. The company's iOS devices account for about two-thirds of its sales.

One customer said Friday that battery life has gotten worse since the software update, while others complained that the battery loses 10 percent of its power each hour.

Apple's shares fell 0.2 percent to $384.62 in U.S. trading. While the stock is still up 19 percent this year, it has lost ground in the past three trading days.