It seems that Apple introduced a nasty battery drain problem with the iOS4.1 update in September. After I installed the update, my iPod Touch 2G drained the battery completely empty after about 8 hours of sleep. Resetting and reinstalling the device didn’t help. The problem was that it stayed connected to the wireless network even in sleep mode.

There exist 2 solutions which seem to work for me so far:

• Switch the iPod into Airplane mode when network access is not needed
• Go to Settings -> Notification settings and toggle all the settings of all applications in that screen to ON and back to OFF. It seems like some these applications have been using wrong settings even with global notification turned off. Toggling the individual settings has reset them to the desired state. You can see if this step was successful by opening the overview of connected WLAN devices in your WLAN access point and then putting your iPod to sleep. It should drop out of the list of connected devices after about 10 seconds of sleep. </ul> Let’s hope that Apple will fix this issue with iOS 4.2 due in November.

Update

The described fix did not prove to be permanent. Every now and the setting seems to reset itself and the iPod stays connected to the WLAN in sleep mode. So back to square one: turn on airplane mode whenever Wifi is not needed. Damn!