This is what I did to fix it. I hope this works for most of us.
Settings General -> Reset -> Erase All Content and Settings -> Enter your passcode
Now everything appeared to be out of the box wit iOS 6.1.2
Restored from backup (not as new) including all email accounts. Turned off the following from exchange accounts (Contacts, Calendars, Reminders). Also Changed Fetch New Data to Fetch every 30 minutes. This has stopped the overheating and battery drain.
I'm currently testing each service to see if I could isolate the problem.
I have the same issue since I updated to 6.1.2. I followed cmarquez24 instructions and i am in the process of recharging the phone it is up to 73% and the phone isnt getting hot like it was. I hope this solves the issue my battery was only lasting about an hour maybe 2 at the most after the update.
I have an email account that uses exchange for email and it uses the calendar. After 6.1.2 the battery issue popped up on my phone. Here is what I did to fix the battery drain problem. Go to "Settings", then to "Mail, contacts, calendars" and select your email account. Turn off calendars, you will get the "this will delete all stored calendar information" message. Say yes, dont worry, you will get it all back in a few minutes. Do a soft reset on the phone. Power it down, let it stay off for 10 seconds. Then power it back up again. Go back into the settings and turn on the calendar for that account. Hopefully this solved your poblem, it did for me.
I called Apple customer support to explain the issue. For my case the problem is with the Exchnage server connection for my work email. It seems that after 6.1.2 the communication between the server and the iPohne drains the battery. I am not sure if it is related to recurrent appointments or not. Here is what Apple support asked me to do although I am not happy about it and it seems that the issue should be looked into and whatever software bug is causing it should be fixed.
1. Go to settings
2. Go to Mail, Contacts and Calendars
3. Go to Fetch New Data
4. At the top of the screen turn the Push off
5. At the bottom of the screen select manually
What that does is it only connects to the server (Exchange) when you actually open the email application. Instead of the emails being pushed from the server to the phone as they arrive and you seeing the counter of new messages displayed next to the mail app youwill see no new messages intul you actually check and wait for about 10-15 seconds for all messages to download to the phone.
So in my opinion whatever the exchange issue with recurring calendar appointments originally prompted the release of OS 6.1.2 is either not solved completely or a new issue was unknowingly introduced. I tested the fix - my battery was at 100% for 8 hours without use.Went dowon to 98% reading some emails for 15 min. Then I truned push on again for 20 min - the battery went down 12% in these 20 min. I turned push off and it laster another 24 hours without a need for rechange with relatively heavy use.
Cutomer support promised to report the issue to developers for futher investigations. Let's hope there will be another OS release soon to correct it.
I'm having the same problem since updating to 6.1.2. However, I did suffer a similar issue in an earlier version of iOS 6 - quick battery drain, but for no apparent reason, it improved suddenly. Until this update. Now it's back and magnified by 4X.
In general, I've become increasingly dissatisfied with the stability and robustness of Apple's iOS. I'm reaching the end of my patience. Apps that crash when they never used to. Flaky call reliability. The still half-baked Maps app. And, since I purchased my "top-of-the-line" iPhone 5, a constant struggle with pathetic battery life. (Just a side note, Apple, but when you have to carry your charger in your pocket too, the iPhone 5 isn't the thinnest iPhone ever anymore)
I wrote this in another thread about this same problem (there are several). I'm reposting it here because I'm hoping that someone in Apple is viewing these forums:
Here's my problem with all of this nonsense. I'm a very experienced Apple user. I have at least one, and usually more than one, of just about everything Apple makes. I'm a Mac evangelist. Why have I become so devoted? Because Macs work. Apple stuff just works. Or it did.
Now, I'm having the same issues since upgrading my iPhone 5 to OS 6.1.2 as all of these people. I shouldn't have to do restores, restarts, hold my tongue just right, or chant magic spells to make my iPhone work reliably. I haven't hacked my phone. I purchase all of my apps via the Apple app store. I do updates asap. My phone should work.
Apple needs to fix this. When you make people, that are as crazy about Apple stuff as I am, start considering Android, you've really screwed up. I need my phone to work when I need it. I rely on it for my work. I count on it for keeping me in touch with ailing family members who may need my help at any time.
If Apple is no longer in the business of supplying reliable phones, then I'll soon take my business elsewhere.