About Swisscom Carrier Bundle 22.1, iOS 9.1 and iPhone 6S battery drain — 28 Oct 2015

@Swisscom_Care it looks like WiFi Calling is draining my battery (iPhone 6s/iOS 9.1) “Settings” is responsible for 80% battery usage :/

— David Roessli (@roessli) October 28, 2015

2015-10-30 : Swisscom's latest Carrier Bundle v22.2 seems to correct the battery issue.

Swisscom's latest Carrier Bundle (v22.1 at time of writing) is proving to be troublesome to Apple iPhone 6S owners running iOS 9.1.

Swisscom's new Advanced Calling features include WiFi Calling which enables you to make calls over both the mobile and WLAN network. Which is cool per se except that it kills your battery in no time.

This problem seems to occur if you have enabled WiFi Calling once (Settings > Phone) -- and remains even if you have turned if off after.

The phone run warm all the time (even when idle), and hot when using it. Checking the Battery usage (Settings > Battery) will display the “Settings” app and the one using up the most battery (80% in my case).

Swisscom acknowledges the issue, and states that Apple is working on a fix.

@roessli 1/2 22.1 is the latest version for this device. Apple is testing a potential solution.

— Swisscom_Care (@Swisscom_Care) October 28, 2015

A workaround is to downgrade your Carrier Bundle as explained by mjoe on Swisscom's Community Forums : http://supportcommunity.swisscom.ch/t5/Diskussionen-rund-ums-iPhone/iPhone-6s-und-6s-Plus-Carrier-Probleme-mit-iOS-9-1/td-p/405197/page/9#messageview_2
Source Twitter.

How to downgrade your Carrier Bundle (Swisscom)

1. Make sure that iTunes Carrier Switch is set to YES;
2. On a Macintosh computer open the Terminal app and type: defaults write com.apple.iTunes carrier-testing -bool YES
3. On a Windows computer, open the command prompt and type: "%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt carrier-testing 1
4. Download a previous Swisscom Carrier Bundle (v22.0 or 21.2) IPCC file from Apple's servers: http://appldnld.apple.com/ios9/carrierbundles/031-42631-20151021-EC8608E2-76C1-11E5-B2FD-503E40B99175/Swisscom_ch_iPhone.ipcc
5. Connect your iPhone to your computer, and open iTunes;
6. Transfer the bundle via iTunes by alt-clicking on “Check for Updates” and selecting the IPCC file you have just downloaded;
7. Your iPhone should now display the version of the bundle in Settings > General > About > Carrier (e.g. Swisscom 22.0);
8. Beware NOT to accept new settings when our iPhone tells you that new settings are availble, otherwise you'll be back to square one.

A BIG thanks to mjoe for providing this hotfix!

Caveat: if you have Carrier Bundle 22.1 installed, but have never turned WiFi Calling on, it doesn't seem to occur (tbc).

Source: XML feed of all the Carrier Bundles available from Apple.