"A recent update to Google maps and Google now (Google search) has been causing a lot of battery drain issues."
Yep - the Apple Genius warned me about Google Now.
In the testing I did a couple years ago, I found that having the GPS continuously active takes about 5% per hour. Any app that uses GPS will be a drain. Most conservative solution is to turn off Location Services for all apps that you are not actively using while in the backcountry. Also, you'll want to turn off the sneaky Location things:
Privacy->Location Services->System Services (all the way at bottom of Location Services): Everything OFF (except Compass Calibration which is useful when hiking). You really don't need the phone to track your location so it can feed you location-appropriate advertising :(
I've done enough testing, and gathered feedback from enough people, to draw conclusions. I will update the primary article when I get a half day to rewrite things. In the meantime, please spread the word to your friends who care. All advice assumes you will be outside signal range and want to use the GPS. All data assumes you have done all battery conservation measures described in the original post of this thread: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=80978
ATT iPhone 4: You should remove the SIM or use the SIM PIN feature to lock the SIM. Result (when combined with all other battery saving steps) is 1-2% drain per day.
ATT iPhone 5: Removing or locking the SIM is a bloody disaster causing drain of 10% per hour when there's no ATT signal -- therefore you must leave the SIM active! This is clearly a bug in the interaction of the hardware, firmware, software, and/or SIM. There's no good solution for using the phone outside ATT signal range and with Airplane OFF. Best option: leave the SIM active and put the phone into Airplane Mode when not actually using GPS. Expect a drain of 22% per day when 1) outside signal range, 2) SIM active, and 3) airplane mode OFF. With Airplane mode ON the drain is reduced to 4% per day.
iPhone 5 with GSM and CDMA (i.e. Verizon, Sprint): They have no problem if the SIM is removed or locked. (I am unclear on their battery drain if the SIM is active and will update the info if I learn more.) My brother did a very controlled test: SIM removed, Airplane mode OFF, no signal, all other battery conservation measures in place -- he lost 1% battery in 12 hours. DanS did a 9-hour controlled test (although didn't disable all other battery-draining features) and had very modest drain. Several people reported modest drain in backcountry usage, although they did not have controlled test results.
If I didn't already own an ATT iPhone 5 I would definitely choose the Verizon model. It is too risky, IMHO, to rely on engaging Airplane Mode every time I want to use GPS.