[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] pshah:
Network switching and battery drain

So I have also been experiencing the random battery drain (10-20%/hr) and overheat of battery that many people have been talking about here and other places, that appears to be triggered by something unknown, and will drain until you reboot. All with Sync, wifi, data, screen, GPS off, and mostly just stock apps.

I am on AT&T in Chicago, and changed from LTE (PTA) to HSPA network but setting up an APN "wap.cingular". This does not require root, and got the idea from somebody on AT&T forum who got it from AT&T support themselves. Verified I was on HSPA through Settings->About Device->Status, along with not having "4G LTE" just "4G" when I turn on data, and of course, much slower data speeds.

Since then (2 days) have not had any random battery drains (10-20%/hr), and have been able to use everything normally (phone, data, wifi, GPS). By now, on LTE, would have definitely had at least one battery drain occur. I will keep on HSPA and write again if I do experience a drain. I suspect that the battery drain is triggered by the phone trying to change networks from LTE and HSPA and not being able to do so.

Further evidence of this: on a prior xda post (http://xdaforums.com/showthread.php?t=1791955&page=2), somebody discusses how LTE does not carry voice and AT&T puts you in LTE on standby and then switches to HSPA when a call comes in and then back when you are done. I remember 2-3 battery drains being triggered by a phone call. Other times, when I had bad signal, the network changed from LTE to HSPA also (in Settings->About Device->Status) This could explain the randomness of the drains.

Also, I randomly searched and found some highly technical papers that seemed to say it is hard to negotiate the change. 2G/3G changes are easy, but LTE to 3G/4G is not that easy. Also, when I switch networks manually, through settings and selecting APN, the battery heat up and drain start. So, I do believe that this is the cause, will continue on HSPA to make sure. On HSPA also the standby battery life is incredible (1% overnight -- with sync on, no data)

So I do hope the solution is in the works, really got used to LTE speeds. You can of course, switch to LTE network by going into the settings and changing, but takes 4-5 extra clicks. Hopefully some OTA ROM update, which jeffrei posted previously, or the Voice Over LTE that is hopefully coming (http://www.eweek.com/c/a/Mobile-and-Wireless/Samsung-Galaxy-S-III-Now-Supporting-VoLTE-392288/) so the phone would not have to constantly change networks with every call.

Other things I don't know -> There are settings on the GSAM app, international versions of the phone, and I believe the Verizon phones in the US, that talk about LTE RAM dumps, enabling SMS over IMS. If anybody knows more about this, or a toggle that works on AT&T that allows quick switching of networks (which I believe AT&T does not actually allow), would be great.

Hope this helps people. To set up new APN...go to Settings->Wireless and Network Settings: More Settings ->MObile Networks->Access Point Names. Then menu button, New APN, and under APN add "wap.cingular" and whatever Name you want. I think I had to wait or reboot after or something.