When an iOS device is connected to WiFi and charging, it sometimes downloads iOS system updates in the background. These downloaded updates take gigabytes of space that cannot be reclaimed! This is how to prevent/fix this problem (Apple probably considers this a feature, bullying users into upgrading to reclaim lost storage space). To prevent updates from automatically downloading: 1. Fill up you iDevice with as much data as you can. I think getting the free space under 600 MB is sufficient, since system updates are at least 700 MB. It can be any kind of data, but I find music and self-shot videos are easy to delete quickly if you need space (to download an app or shoot video for example). To delete an update that has already been downloaded: 1. See step 1 above. 2. Wait for an update from Apple (7.0.3 is rumored to be released in the coming weeks). When the update becomes available, disconnect from WiFi when charging. 3. Within a week, the iOS device will check for updates and delete the previously downloaded update. As soon as this happens, fill up the cleared space with your own music, movies, data, etc. 4. When you need more space, delete the extra data you added, making sure to keep under 600 MB free when you charge your device. Don't forget to tell Apple to STOP the automatic background downloads of updates. It's your device, you should have complete control of what's on it! http://www.apple.com/feedback/ Edit Oct 24: Here is the feedback I sent Apple. Feel free to copy/paste! The iOS 7 update downloaded automatically to my iPhone, using my limited internet bandwidth, and more importantly using up space I could have better used for music, movies and apps. This is unacceptable. I paid lots of money for my iPhone, I own it, so Apple shouldn't download a permanent, undeletable waste of disk space without my consent. A simple toggle in the update panel "Download updates automatically - On/Off" is all that is needed.