Q: I found out why iCloud backups are failing (iOS 7 on multiple devices)

For some time I have been observing that automatic backup sometimes works, and sometimes doesn't.  After some experimentation, I think I have figured out.

It makes a difference whether the battery is fully discharged before I plug in the device for recharging.

If the battery still has a partial charge, then automatic backup works as it should.

However, if the battery is fully discharged, thus requiring a cold restart, then the backup does not happen UNLESS I actually unlock the device and then lock it again while it is charging.

In other words, it is not sufficient merely to have the device plugged in, connected to wifi, and locked. It is not sufficient if the device wakes up from a cold boot and passively enters a locked state, because this state does not trigger a backup.  It is necessary to actively lock the device (wake it up and then put it to sleep again) in order to get a backup.

I have been experimenting with this on an IPhone 5, an iPhone 4, and and iPad, all running iOS 7, and I have consistently found this behaviior to hold in all cases. This was not happening under iOS 6.

Dave Seaman