Hi Everyone,
I managed to get 10.0.2 sorted and working with great battery life (back to how it was as a brand new iPhone 7 when on 10.0.1 with average of 36 hours switched on (6-8 hour usage reported in battery settings).
I am copy-pasting the text reply I recently sent to Apple Bugreporter - In the process of trying to reproduce the bug and logging for Apple I actually fixed the battery drain issue!
Before I copy paste, I will give you all the short summary (Do this at your own risk to data loss) -
Super-short summary
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Fixing the battery drain issue on 10.0.1 may be accomplished by:
1. Backup of iPhone/iPad
2. Resetting all settings + Resetting Network Settings
3. Download only of iOS 10.0.2 in iTunes (do not select Download & Update) and then do "Restore iPhone" in iTunes - NOT OTA Update
Short summary - If above doesn't work you may need to introduce downgrade of iOS into the steps...
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1. Avoid OTA Update.
2. If you have updated to 10.0.2 and experience the issue, downgrade to 10.0.1 using iTunes Restore (see instructions on loading 10.0.1 IPSW and make sure to backup first)...
3. Once on an iOS version below 10.0.2, Reset all settings and (very importantly) Reset Network Settings (in Settings-General-Reset).
4. Using iTunes "Backup" (If at any stage you are prompted to Download & Update iOS, just select "Download only")
5. Using iTunes, connect iPhone/iPad and click the Restore iPhone button - At the end of the process select your backup to restore all your old data and settings.
COPY PASTE OF REPORT:
* iPhone 7, 10.0.1 -> 10.0.2 OTA Update
* 50-70% of previous battery life observed over 48hr period
* Tried a restore from iTunes (10.0.2 -> 10.0.2) - no change in battery drain issue
* iTunes Backup
* Downgraded (Using iTunes restore) to 10.0.1 - battery drain mostly returned to normal but seemed to still be down a little but this is hard to say as my usage does vary...
* Factory reset (settings only) and Network settings reset carried out
After being asked to submit bug report took the following steps:
* iTunes Backup
* Using iTunes upgraded 10.0.1->10.0.2 using the "restore iPhone" method and then selecting my latest backup
* Noticed towards the end of the restore process I was prompted to Install "Carrier Settings Update). This did not happen during the previous OTA Update (or downgrade).
On this point, I do feel this may be a clue to the cause of the battery drain issue (corrupted network settings during update). Another iPhone customer reports the same result:
https://discussions.apple.com/thread/7666765?start=90&tstart=0
quoting ellab318:
"I did a full reset to my iPhone 6 (Verizon) and it was successful. When I reset the phone it also prompted me to update my carrier setting, which may have been part of the problem. After the full reset and restore my battery usage is as it was prior to IOS 10.0.1 (now 10.0.2) and it has not overheated once..."
Good Luck and hope you cure your iOS 10.0.2 probs...