Battery life is very good for iPhones

Expect to get between 5 to 10 days of battery life in the field (we usually get 7 or better) without recharging. Our normal daily use of the following: use the iPhone’s GPS for a few locations, looking at electronic maps, taking a few photos, and some reading of electronic guides/references. Even so, we bring a backup battery just case we need to use the GPS more or do something silly that drains the battery.

Always Bring a Backup Battery!

It’s a critical safety precaution to make sure your smartphone is always available for use as a GPS. My three favorite lightweight and high capacity backup batteries are:

Anker PowerCore 10000 (only 6.4 oz) is Amazon’s most popular USB Battery is the lightest option if you need to recharge your phone a lot. It can charge a large phone like a Galaxy S7 ~2.5x and a smaller phone like an iPhone 7 ~3.5x.The 5.4 oz Jackery Bolt 6000 mAh USB Battery With two built-in cables (lightening & micro-USB) it will charge just about any backcountry electronics. It has a faster charging rate than the EasyAcc below but has slightly less overall capacity. EasyAcc 6000mAh USB Battery This has slightly more capacity (tested) than the Jackery battery but has a slower charging rate and only a built micro-USB cable (altho you can attach your own lightning cable to charge an iPhone). It can charge a large phone like a Galaxy S7 about 1.4x and a smaller phone like an iPhone 7 2.3x.

Battery Life for Android Phones

Not a show stopper, but Android phones appear to have less battery life on-trail than iPhones—more in the range of 3-5 days with moderate GPS use. This seems to be in part due to differences between Android smartphones for both a) the phone hardware and b) variations of the Android OS on installed on phones. As such, the Android environment is not as easily understood/managed vs. tightly controlled, and very predictable iPhone hardware and iOS environment. This makes Android battery management more challenging. Nonetheless, an Android smartphone is a valid & capable backpacking GPS.

Cliff Notes – a jump start to use your smartphone as backpacking GPS

Battery life management 101

Expect: Between 5 to 10 days of battery life in the field for an iPhone with moderate use of GPS, mapping, taking a few photos and use of electronic guides/references. And around 3-5 days with “conservative use” of GPS with an Android phone like a Samsung Galaxy (newer models like the S8 or S9 may do better but you’ll need to test to confirm this)

Do: Put your smartphone in Airplane Mode and leave it there for the duration of your trip. For iPhones, the GPS will work in Airplane Mode as of iOS 8.3.



Do: put your screen in auto-brightness, and lower your screen brightness to the minimum amount. Screen power is the single biggest battery drain for your phone.

Do: Shut Down all unnecessary apps especially ones like Google Maps and Facebook that use location tracking (the GPS) in the background. (See more tips below for “Battery Conservation Settings” below)

Do: set your GPS App to only get a GPS fix when you manually request it.

Use Tracking mode in your App with discretion. It will drain your battery by about 2% to 5% per hour. Note: the current version of GAIA on the iPhone 6+ or 8+ only uses around 2% per hour. This makes it a viable tracking took for trips of 3-4 days (and even longer if you bring a good USB battery to re-charge it.)

Good Idea: to test your personal battery use on a couple of long day hikes before taking the smartphone for navigating on a long trip.

See more tips below for “Battery Conservation Settings” below

Download Maps into GAIA For Offline Use on the trail where WiFi and cellular data are not present — but where the smartphone GPS still works. On the left is a partial list of map sources for download. On the right the pink box indicates the area of the map selected for Download from a Rectilinear Area. You can also use the “Download Maps for Track” feature which automatically gets all the maps needed to follow a line, a phenomenally useful feature when setting out on a thousand-mile hike or paddle. Download Maps for Track and the wide range of map types are the two features that make Gaia GPS stand head and shoulders above the other available apps. on the trail where WiFi and cellular data are not present — but where the smartphone GPS still works. On the left is a partial list of map sources for download. On the right the pink box indicates the area of the map selected for. You can also use the “” feature which automatically gets all the maps needed to follow a line, a phenomenally useful feature when setting out on a thousand-mile hike or paddle. Download Maps for Track and the wide range of map types are the two features that make Gaia GPS stand head and shoulders above the other available apps.

Battery life in the field for iPhones

From my friends and accomplished long-distance hikers, Amy and Jim:

Our daily use of the iPhone includes 5-50 sessions with a mapping app (depending on how ambiguous the route is), 10-20 photos, occasional use of bird guide apps, alarm clock, checking time, reading Wiki Offline, and nightly journal entries. All of our usage is discretionary except for the mapping apps and GPS reads. We scale our discretionary use based on how many days remain before the next recharge opportunity. With restrained use, most models of iPhones (especially the iPhone 6 Plus, 8 Plus or X) will last for a week or even ten days. If we only have two or three or four days to the next recharge opportunity, then we take more photos, play more bird calls, etc. Your mileage will depend entirely on your usage patterns. Prior to a multi-day trip, be sure to establish your baseline drain (iPhone asleep and no activity) to make sure that drain is minimized as described in the Battery Drain section. Experiment on day hikes so you can estimate your daily drain based on your own usage patterns.

Baseline iPhone battery drain is 1-3% per day

When all battery conservation measures are in place, the baseline battery drain (phone on, but not in use) of most iPhone models is 1-3% per day. Without proper battery conservation measures, the daily baseline drain will be at least 10% and often over 30%. By baseline drain, we mean that the phone is powered on, but asleep; it is ready for use, but the user is not actually doing anything with it. This is the background drain you will incur even if you don’t take any pictures, look at any maps, or use any apps at all.

Battery Conservation Settings for Android or iOS Smartphones

It’s important to follow these guidelines to conserve your iPhone battery and get the maximum battery life in the field. For day hikes or overnight hikes most of these suggestions are not as important, but they are critical if you want to use an smartphone for a multi-day trip without resorting to a recharge solution (external battery or solar). Our research ended up focusing a great deal on battery life, and we hope these ideas help.

Settings to Optimize Battery Life – iOS and Android Smartphones

This is a list of major settings to increase your battery life. These settings apply to both iOS and Android. In the case of iOS we have included the menu path to change the setting.

Major Settings

Monitor your battery charge percentage. iOS: General->Usage->Battery Percentage = ON.

iOS: General->Usage->Battery Percentage = ON. Airplane Mode = ON . WIFI = OFF. Bluetooth = OFF (unless connected to something like your Delorme inReach). AirDrop = OFF. Personal Hotspot = OFF [for iOS these are all in the “Control Center” (swipe up from the bottom of the screen)]

. WIFI = OFF. Bluetooth = OFF (unless connected to something like your Delorme inReach). AirDrop = OFF. Personal Hotspot = OFF [for iOS these are all in the “Control Center” (swipe up from the bottom of the screen)] Minimize screen brightness and screen use. A bright screen is a significant battery drain. So to minimize battery drain you should make sure the screen is not brighter than necessary. For iOS: Wallpapers & Brightness – Auto-Brightness allows the screen to adjust its brightness based on current lighting conditions. Then still use the minimum brightness necessary to use your smartphone.



A bright screen is a significant battery drain. So to minimize battery drain you should make sure the screen is not brighter than necessary. For iOS: Wallpapers & Brightness – Auto-Brightness allows the screen to adjust its brightness based on current lighting conditions. Then still use the minimum brightness necessary to use your smartphone. Check which Apps have the biggest battery drain. You can do this in iOS via Settings->Battery and look under “Battery Usage”

You can do this in iOS via Settings->Battery and look under “Battery Usage” Shut down unneeded apps. Most apps do nothing while in the background and it is fine to leave them in this inactive state. A few apps (i.e. mapping apps that have engaged the GPS in Tracking mode, Google Maps, and even Facebook) can activate the GPS in background and drain your battery. In theory, if an app is using the GPS there will be a small GPS Location Icon (arrowhead shape) at the top of the screen; e.g. this icon appears when Google Maps is active in the background. But the GPS Icon is not a 100% reliable indicator, so you need to ensure that unneeded apps that might be running the GPS are fully shut down before you start your trip. Here are instructions on how to shut down background apps. (For tech-weenies, here is an article that offers a more complete explanation.)

Most apps do nothing while in the background and it is fine to leave them in this inactive state. A few apps (i.e. mapping apps that have engaged the GPS in Tracking mode, Google Maps, and even Facebook) can activate the GPS in background and drain your battery. In theory, if an app is using the GPS there will be a small GPS Location Icon (arrowhead shape) at the top of the screen; e.g. this icon appears when Google Maps is active in the background. But the GPS Icon is not a 100% reliable indicator, so you need to ensure that unneeded apps that might be running the GPS are fully shut down before you start your trip. Here are instructions on how to shut down background apps. (For tech-weenies, here is an article that offers a more complete explanation.) For all apps still running, minimize the use of Locations Services (i.e. GPS use). iOS: Privacy->Location Services = ON but Turn Location Services OFF for any app that you will be using while backpacking unless it is important for that app to have a GPS read. For example, if you use a Camera app and you want it to put a GPS stamp on each image, then leave Location Services on for that app. However, if you don’t care about having a GPS stamp on the image, then turn Location Services off for Camera app so that it does not engage the GPS (and therefore drain battery) every time you take a photo.

iOS: Privacy->Location Services = ON but Turn Location Services OFF for any app that you will be using while backpacking unless it is important for that app to have a GPS read. For example, if you use a Camera app and you want it to put a GPS stamp on each image, then leave Location Services on for that app. However, if you don’t care about having a GPS stamp on the image, then turn Location Services off for Camera app so that it does not engage the GPS (and therefore drain battery) every time you take a photo. Don’t use Tracking Mode (if you need trip tracking use a DeLorme inReach or a SPOT Satellite GPS Messenger .) Most smartphone mapping apps like GAIA have features to record a track as you walk, or to guide you to a specified waypoint. But to do this the app must constantly get a GPS read, which is a steady battery drain. So if you are on a multi-day trip, don’t use tracking mode (and use guide me sparingly in GAIA and other apps only when needed). Most of the time, it’s best to manually get your current location when necessary. [In our battery tests we found that Tracking mode consumes ~5% of the battery capacity per hour.]

(if you need trip tracking use a or a .) Most smartphone mapping apps like GAIA have features to record a track as you walk, or to guide you to a specified waypoint. But to do this the app must constantly get a GPS read, which is a steady battery drain. So if you are on a multi-day trip, don’t use tracking mode (and use guide me sparingly in GAIA and other apps only when needed). Most of the time, it’s best to manually get your current location when necessary. [In our battery tests we found that Tracking mode consumes ~5% of the battery capacity per hour.] Set your GPS mapping App to only get a GPS fix when you manually initiate it. Some apps like GAIA have excellent battery management (GPS use) settings, but some do not. I have GAIA set to only engage the GPS when I click the location icon.

Some apps like GAIA have excellent battery management (GPS use) settings, but some do not. I have GAIA set to only engage the GPS when I click the location icon. Keep the iPhone at a reasonable temperature. Batteries achieve optimum service life if used at 20°C (68°F) or slightly below. Avoid letting the iPhone overheat in direct sun, and keep it in pocket close to your body in cold conditions. More detailed battery information in this great article.

Batteries achieve optimum service life if used at 20°C (68°F) or slightly below. Avoid letting the iPhone overheat in direct sun, and keep it in pocket close to your body in cold conditions. More detailed battery information in Optionally shut down the phone at night. We never fully shut down the phone while on a trip, but if your particular phone has a measurable overnight drain you could consider shutting it down every night to conserve battery.

If you need to leave Airplane Mode On (iOS only)

The following iOS settings should be irrelevant when Airplane Mode = ON. They are relevant only to people who choose to keep Airplane Mode OFF for some reason but want to maximize battery conservation. Use any of these as appropriate. Cellular->Cellular Data = OFF

iTunes&App Stores->Automatic Downloads = OFF and Use Cellular Data = OFF

Notification Center – turn off notifications for all apps – No sounds, no badges, no alerts, no nothing.

General->About->Diagnostics and Usage = Don’t Send

General->Background App Refresh – You can disable each app from doing work while it’s in the background (i.e. not open and visible on the screen). Turn OFF everything that you won’t need to have running in the background while on your trip. For example, you won’t need the Stocks app trying to updated stock prices while you sleep!

Mail, Contacts, Calendars: Fetch New Data -> Push = OFF, and Fetch = Manually

How to Choose your Mapping Apps

International mapping 1: Gaia GPS displaying OpenCycleMap of a section of the Lycian Way in Turkey. Red lines and blue pins show our intended route (2 alternatives shown). The brown dashed lines show trails that have been added by users to the OpenStreetMap database, wiki-style. OpenCycleMap and Satellite imagery are especially important when hiking in Turkey because the government does not publish any topographic maps. Using an iPhone with a $20 app (in this case Gaia GPS) we carried maps, satellite imagery, and track data for ~600 miles of trails in Turkey! Gaia GPS displaying OpenCycleMap of a section of the Lycian Way in Turkey. Red lines and blue pins show our intended route (2 alternatives shown). The brown dashed lines show trails that have been added by users to the OpenStreetMap database, wiki-style. OpenCycleMap and Satellite imagery are especially important when hiking in Turkey because the government does not publish any topographic maps. Using an iPhone with a $20 app (in this case Gaia GPS) we carried maps, satellite imagery, and track data for ~600 miles of trails in Turkey!

Before choosing an app, you need to decide which types of maps you want to view while hiking. You may want to use more than one app if you care about more than one map type. After deciding which map type you want you can then evaluate the features and usability of the apps that provide that map type. Here are the general classes of maps:

National Mapping Agency maps – Topographic maps issued by the government that provides coverage for an entire country (USGS, NRCan, OS, IGN, LINZ, etc). These maps are almost always the most accurate and detailed source of topographic and geographic information, although they often do not have the most current cultural changes, such as new trails. Some governments license their map data to the apps at no charge (USA, Canada, New Zealand, and some UK maps), and others do not (UK’s best maps, France, Australia).

When you use an app that gives access to freely licensed maps (for example USGS) you usually do not need to pay any fees (beyond the initial cost of the app) to download an unlimited amount of map data. When you use an app that gives access to maps for which the app developer must pay licensing fees, then you will need to pay for the map content. Prices vary wildly, depending on the fees that must be paid to the government for use of the maps. For example, iPhiGeNie charges 15 Euros per year to access the all maps that IGN publishes (not so bad); ViewRanger charges 90 GBP for the 1:50K LandRanger series, the Explorer series is additional (wow!).

For access to USGS, NRCan, and LINZ (USA, Canada, and New Zealand) maps we recommend Gaia GPS. Gaia GPS provides Satellite imagery and OpenCycleMaps in addition to the National Agency maps and has a rich set of features. Plan to spend at least an hour learning how to use it, as some of the important features are not obvious. (Someday I will write a concise introduction to Gaia for backpackers, as many of the features are geared to day-hikers and should be ignored for backpacking.) For a user who wants the most complete set of functionality and the best selection of map sources, this is the best available app for the US, Canada, and New Zealand.

International mapping 2: A section of the GR20 in Corsica France using the iPhiGéNie App. There is no substitute for getting access to the Official National maps; they are the highest quality.

For access to the National Mapping Agency maps of Europe, we are not experts but propose the following.

iPhiGéNie (both an initial cost and cost for map access) is the best alternative for Catalonia, Italy, Germany and Norway and an good option for France, Spain. Based on our use of iPhiGéNie on the GR20 in Corsica France, this App is the equal of Gaia in features, performance, and battery conservation. ( Note: France & Spain IGN maps also in GAIA for a fee as of May 2016

ViewRanger is a solid full-featured app that offers the gold standard Explorer and LandRanger OS maps of the UK as well as National Agency maps for most European countries. We used ViewRanger for a long hike in Scotland and it was solid and met our needs. This app offers USGS maps as well as maps of Europe, however, the usability and feature set are not as good as Gaia GPS and therefore we do not use it the US.

UK Map offers freely licensed OS maps, which are not as detailed as the Explorer and LandRanger series but will suffice for many users (especially price-sensitive users).

It is elegant and easy to use but does not support waypoints or tracks.

OpenCycleMap – aka, OpenStreetMap, OSM, OSM Topo, Cloudmade Topo/Cycle, OpenHikingMap. Many iPhone apps include this map source because it is a freely licensed topographic map of most of the world (below 60 degrees latitude).

Although the topographic and geographic detail is not as good as maps from the national mapping agencies, there are three important characteristics: it is freely licensed; cultural information is often more current, and it covers most of the world.

Take a look at the OSM treatment at their website . We have successfully used OpenCycleMaps together with Satellite imagery (with no National Agency Maps) for long hikes in Turkey, Australia, and Spain. In Turkey there were no National Agency maps available; in Australia and Spain they were available but at too high a cost for our purposes. Gaia GPS is our favorite app for this map type. There are many other apps that provide access to OpenCycleMaps, but only Gaia (that we have found) also includes downloadable worldwide Satellite Imagery, is easy to use, supports waypoints and tracks, and allows import and export of gpx and/or kml files.

– aka, OpenStreetMap, OSM, OSM Topo, Cloudmade Topo/Cycle, OpenHikingMap. Many iPhone apps include this map source because it is a freely licensed topographic map of most of the world (below 60 degrees latitude). Although the topographic and geographic detail is not as good as maps from the national mapping agencies, there are three important characteristics: it is freely licensed; cultural information is often more current, and it covers most of the world. Take a look at the OSM treatment . We have successfully used OpenCycleMaps together with Satellite imagery (with no National Agency Maps) for long hikes in Turkey, Australia, and Spain. In Turkey there were no National Agency maps available; in Australia and Spain they were available but at too high a cost for our purposes. is our favorite app for this map type. There are many other apps that provide access to OpenCycleMaps, but only Gaia (that we have found) also includes downloadable worldwide Satellite Imagery, is easy to use, supports waypoints and tracks, and allows import and export of gpx and/or kml files. Satellite images – Often very useful, especially for off-trail hiking. Gaia GPS is our favorite app for satellite imagery as it offers downloadable satellite imagery of the whole world (3 different sources: Mapquest, ESRI, Google).

– Often very useful, especially for off-trail hiking. is our favorite app for satellite imagery as it offers downloadable satellite imagery of the whole world (3 different sources: Mapquest, ESRI, Google). Regional and local maps – Nearly every park publishes a map showing park boundaries, trails, roads, campgrounds, and points of interest. These will nearly always have the most current trail information. Maplets is a great app for viewing these maps; if the park you want is not already available, submit a request and they will attempt to add it. You could find these maps on your own, and view them using any iPhone pdf viewer. However, Maplets makes it very easy to find them, and by using Maplets you are able to see your current location on the map (for those maps that were drawn to scale). Maplets includes limited ability to import, create, and export tracks and waypoints, so you will probably end up using it in conjunction with a more fully-featured app like Gaia GPS. In addition to park maps, Maplets has a rich inventory of maps of transit systems, bike routes, airports, museums, university campuses, etc. (Of all the apps I’ve used, Maplets is the one I most wish I had imagined and then produced; it is an elegant, simple, useful, concept that is very well executed.)

Tips on Using the iPhone

Regardless of which app you choose, there are a few considerations for using an iPhone in the backcountry.

Data – When you have a WIFI connection, download the map content (and trail data if you have it) that you’ll need while hiking. Your iPhone can get a GPS signal in the woods, but you will be unlikely to reach the Internet for data. Battery Life – Manage your battery life. Day hikers can get away without taking special steps to tend the battery life, but for multi-day trips, you must tend to these things. This article closes with detailed instructions on how to maximize battery life. Protect Your Phone – In terms of waterproofness and durability, the iPhone needs to be treated as you would treat a non-waterproof camera, unlike a Garmin which is designed for outdoor conditions. It can be “waterproofed” with a 5 gram $0.15 Pint Ziploc Freezer Bag , a more expensive Aloksak 4.5×7″ ziplock, or an expensive LifeProof case. Even when it not raining, we keep the iPhone in a pint zip lock to protect it from sweat and dirt. LifeProof makes low-profile light-weight completely waterproof cases, which might be an good option for very wet environments. OpenStreetMap – Spend an hour learning about OpenStreetMap (aka OSM). OSM is a free map of the world, and many iPhone apps are based on map content from OSM. OpenCycleMap (aka Cloudmade Topo) is a variation that includes contour lines and hiking trails. Data is added to OpenStreetMap by users like us, wiki-style. If your favorite trails are not there, then you can add them and the world will be a better place for it.

Protection for iPhone: We highly recommend using a Pint Ziploc Freezer Bag used to protect your smartphone from dust, scratches, and water (effective, lighter and less expensive than elaborate waterproof cases! Works well for other electronics.).

Detailed Testing and More Information on iOS Hardware Models

This a very technical and detailed section that supports the summary information above. I will likely only be of interest to technophiles, but here it is:

For purposes of this article (GPS and mapping), the iOS devices vary in only two ways: GPS Chip and Battery Drain. First, some iOS devices have a GPS chip and some do not.

A device with a GPS chip can identify your location (usually within 10 or 20 meters) even when it has no WIFI or Cellular signal.

A device without a GPS chip can identify your approximate location only when it has a WIFI signal; these devices are still useful tools for looking at maps but will not show your location on the map while you are hiking.

a GPS chip can identify your location (usually within 10 or 20 meters) even when it has no WIFI or Cellular signal. A device a GPS chip can identify your approximate location only when it has a WIFI signal; these devices are still useful tools for looking at maps but will not show your location on the map while you are hiking. All iPhone models (4, 4S, 5, 5C, 5S, 6, 6+) include a GPS chip.

models (4, 4S, 5, 5C, 5S, 6, 6+) include a GPS chip. No iPod-Touch model has a GPS chip.

model has a GPS chip. All iPad models that have 3G or Cellular also have GPS chip and therefore behave like an iPhone for mapping purposes.

The WIFI-only iPads do not have a GPS chip and therefore behave like an iPod Touch for mapping purposes.

Second, there are subtle but very important differences in battery drain between the different models and different cellular providers. See the Battery Drain and Different Models of iPhones section below for critical information.

To clarify a common misconception: You do NOT need WIFI or Cellular connection for the GPS chip to work; however you do need to have pre-downloaded the map content in order to have your current location show up on a map.

Battery Drain and Different Models of iPhones

When all battery conservation measures are in place (as per the Battery Conservation Settings section), the baseline battery drain of most iPhone models is 1-3% per day. Without proper battery conservation measures, the daily baseline drain will be at least 10% and often over 30%. By baseline drain, we mean that the phone is powered on, but asleep; it is ready for use, but the user is not actually doing anything with it. This is the background drain you will incur even if you don’t take any pictures, look at any maps, or use any apps at all.

In some configurations, the amount of battery drain depends on whether you are in-range or out-of-range of the cellular provider. Therefore if you test your baseline battery drain at home you are likely to get one result (in-signal-range), while when you use the iPhone in the backcountry you may get a different result (out-of-signal-range). In order to do my battery drain testing, I constructed a Faraday Cage by putting the iPhone inside a closed cookie tin and putting the tin into a microwave oven; neither the cookie tin nor the microwave alone blocked signal. We highly recommend that you run overnight tests at home with your own phone in two test scenarios: in signal range, and in a Faraday Cage.

The most important factor in preventing drain is to disable the cellular activity. The phone will incur ~10% daily drain just maintaining a signal, or 20-30% daily drain searching for a non-existent signal. Starting in iOS 8.3, you can set Airplane Mode = ON, which will disable cellular activity while leaving GPS enabled. This solves many battery management problems that previously existed. All users with an iPhone4S or later model should ensure they have iOS 8.3 (or later), and keep Airplane Mode = ON for the entire duration of backpacking trips.

Based on 64 overnight tests using 18 different phones, we (authors with help from many other people) offer the following guidance about baseline battery drain, assuming iOS8.3 and Airplane Mode = ON.

iPhone 6 and 6-plus: We tested nine different 6/6+ phones (a variety of models and a number of carriers). All except one phone (noted below) had a 10-12 hour drain of 0 or 1%, implying a daily drain <=3%. You can find your model in General->About->Model, and use the information in this excellent TechWalls article to understand the differences between models and to figure out which model you own. iPhone 6 model A1586: baseline daily drain is 3-8%. This phone had a higher drain than any of the other iPhone-sixes that were tested.

Laurie ran 29 different overnight tests on her phone, using a wide variety of configurations (in signal range or not, with ATT or Verizon or no SIM, on the counter or in motion in a pocket), and the ten-hour drain was usually 2-3%, ranging from 1 and 4%, with no discernable pattern. It remains a mystery why this unlocked model in all its configurations had more battery drain than the other models of sixes that were tested. Perhaps it is something in this particular model, or perhaps it is this one particular phone. ATT or Verizon iPhone 4S 5 or 5S or 5C: baseline daily drain is 2-6%. ATT iPhones 4: Prior to iOS 8.3, Airplane Mode toggled both the Cellular Service AND the GPS chip ON or OFF. iOS 8.3 is not available for the iPhone 4, and so these users must leave Airplane Mode = OFF in order to use the GPS. Sadly, when Airplane Mode is OFF, the iPhone, in some configurations, drains the battery trying to establish a Cellular connection. Baseline daily drain:

1-2% per day: SIM Inactive (either locked or removed) (signal either present or absent).

9-10% per day: SIM Active (signal present).

30% per day: SIM Active (no signal).

To maximize battery life of an ATT iPhone 4, deactivate the phone’s SIM by using one of two methods:

Use the SIM PIN feature (read Apple’s Help Topic. and call 611 from your phone to get your initial PIN from ATT). When using this feature, you are asked for the PIN code only after the phone is fully powered down, not after each time the phone has been asleep. This is an elegant easy-to-use solution that gives a great result. Remove the SIM card from your phone. Be careful, the SIM card is small and quite easy to lose

Special Note about using the SIM lock feature in ATT iPhones 5 and 6: In the ATT iPhone 5 and 6, the SIM lock feature has a substantial bug. Unlike the iPhone 4 (where it solves a problem) it is counterproductive in the newer phones, which have more drain with a locked SIM than an unlocked SIM. Fortunately, the newer phones don’t need this feature since they can simply set Airplane Mode = ON.

When the SIM is locked, Airplane Mode = OFF, and there is no signal available, the phone will drain 2-10% per hour !!!!

To maximize the battery life of an ATT iPhone 5 or 6, don’t lock or remove the SIM, as that will cause a disaster when you leave the signal range. Update to iOS8.3 and set Airplane Mode = ON and all will be well. We have not seen this problem reported for Verizon phones, so users with Verizon phones can lock or remove the SIM if desired.