Let me try to be helpful. Whatever the problem is, it is NOT a problem with the specific version (in this case, 10.3.3). If you assume it is a problem with the version you will never resolve it. There are a couple of reasons I say that. The first is that this was a trivial change, adding a few lines of code to block a hacker from taking over the radio chip. There is no way such a small change could have created a battery drain problem.
The more general reason is that in the 10 years and dozens of updates that have been released, there are a small number of phones that report increased battery drain after EVERY update. The number of reported problems for 10.3.3 is an order of magnitude fewer than for several other recent releases, and even those were small numbers. There are only two cases where this was actually a problem with the release; 2.0 and 3.1.0. And the many thousands of posts after each of these releases demonstrated that.
If it isn't the version itself, what causes the sudden change in battery life? Sometimes when a version is installed it causes a problem in an app. The update process terminates running apps, and not all of the 1 million+ apps are coded to handle that gracefully. When they restart they may have lost the status of whatever they were doing. They keep retrying and failing, consuming battery in the process.
Another possible related cause is Microsoft Exchange. There is a flaw in the Exchange ActiveSync protocol. It has been there forever; fixing it would require a protocol change, which would break billions of devices that use ActiveSync. So Microsoft doesn't fix it. If an ActiveSync device loses its place in what it was doing it creates a new connection to the Exchange server. But the Exchange server doesn't know about the problem. It accepts the new connection, but doesn't kill the old one, which keeps trying and failing, again using energy. If you have an MS Exchange account and you have a battery problem (even not associated with an iOS update) either turn off the account in Settings, restart the phone, and turn it back on. Or delete it, restart, and add it back.
In general, go to Settings/Battery and see which apps are using the most energy. Wait at least a day after the update to do this, so you have 24 hours worth of data.
Troubleshooting steps for sudden changes in battery life:
- Kill all running processes, then restart the phone. Note that this will not necessarily fix the problem of stuck apps, however, because they may restart in the same state they were in when killed.
- Connect to iTunes, restore iOS, and restore your backup. This does 2 things: it deals with the possible but unlikely problem that the iOS version on the phone is corrupted, and it also assures that all apps restart fresh. Remember that app data must be restored, which uses energy, so wait at least 24 hours to see if the problem is resolved. If not:
- Repeat, and set up the phone as new. Do not log in to iCloud. Do not install any email accounts, calendars or contacts. Do not install any apps. If the problem is still present after a few hours your phone has a hardware problem.
- If this does resolve the problem try restoring your backup. If the problem comes back you have corrupt data for one or more apps. You can try to figure out which app from Settings/Battery.
