Problem could be triggered by a chance in WiFi behavior in latest update for mobile OS.
Some iPhone users are complaining of their batteries being drained after applying the latest update, iOS 6.0.2.
A number of users reported the problem on Apple's forums who stress that the new update, which was designed to fix WiFi issues, is draining their batteries faster than before.
One user said: "I can usually get through a day with about 75 percent of my battery power remaining. Today I've gone through 90 percent and I've done nothing special with it."
Another stated: "Today I barely used my phone at all, and I noticed I was down to 40 percent after 3 hours of being off the charger. This is a significant change in battery drain."
A third iOS 6.0.2 updater added: "before with the 6.0.1 I didn't have any kind of problem with the battery, I could have my battery full charged without doing any use of the iPhone 5 the whole night keeping 100 percent. But this morning when I woke up the battery was in 91 percent obviously without using the iPhone during the night."
TidBITS authors Adam Engst and Michael Cohen suggest that the problem is possibly caused by a change in the WiFi behavior in iOS 6.0.2. In particular, the latest update appears to have increased the number of WiFi checks it performs to resolve wireless connection issues.