Sarah Tew/CNET

If your iPhone 6S seems to be displaying the incorrect battery percentage, it could be affected by a known bug.

Apple says it is investigating an issue with its iOS software that appears to be preventing the battery percentage icon from accurately updating on the iPhone 6S and 6S Plus. The problem has lead some users to believe they have more battery power remaining than they do.

Shortly after the iPhone 6S and 6S Plus were released in September, it emerged that different versions of the phone had varying battery life, depending on which of two chip variations they had inside. Apple admitted that this was possible, but said the difference in battery life was only between 2 percent and 3 percent.

This latest battery issue might be superficially misleading, but it ultimately doesn't affect the total amount of juice you can get out of the phone on one charge.

The problem seems to be closely linked to the iPhone's clock and is in particular affecting users who have recently traveled through several time zones or manually adjusted the time on their device.

"This was happening to me but I figured out it was me changing the system time. It was freezing the battery percentage. Hasn't happened to me since I stopped changing the time/date," said Reddit user Sonnyspak.

Apple said it "is aware of this issue and is investigating the cause and a solution." In the meantime it advises users affected by the problem to reset their iPhones and then go to Settings > General > Date & Time and ensure that "Set Automatically" is turned on.

It's unknown how many users have experienced the problem. Apple usually pushes out fixes to such issues in the next iteration of its iOS software, but the company has not said when we can expect to see this.

Apple did not respond to request for further comment.