30 comments on “Getting the Most from Your Phone’s Battery

  1. For some Android models (S5 included), a lighter way to go for battery backup is to carry another battery for the phone with you. It has no extra plastic cladding, USB ports, cables, and takes up less space. GL!

  2. Thanks, for the study information. I’ve used a iPhone 5 and 5s while hiking and your data coincides with my field use. I plan on taking a IPhone 6+ on my CDT thru this year. Based on your field testing I have a good feeling on what to expect. I never turned off my phone while sleeping before, always went with the idea that the startup used too much energy. Have you tried it both ways leaving the phone on all night or turning it off?

    • When I did my tests, turning off the phone at night (versus using standby mode) extended the use by about 10%. When your phone is on standby or airplane mode you use about 0.22% to 0.44% of your battery per hour. Turning your phone off during the night will save about 1.5-3.5% of your battery a day versus leaving it in airplane mode. This small savings every night adds up and results in considerable savings.

  3. Thanks for the info. Not exactly on topic, but when using one of your gps/guide apps do you have to have cell service for it to work? Would you leave your phone in airplane mode until you want to use the app then switch out of airplane mode? I’m confused between sat gps and cellular gps could you please explain differences.

    • Mick — our apps do not need cell service to work. The apps use a combination of the phone’s built-in GPS and offline topo maps that you download when you first install the app while you have an internet connection. All the data is stored on your phone. (In order to activate the GPS on an iPhone you have to turn Airplane mode off, but to activate the GPS on an Android device you can leave the phone in airplane mode but separately turn the GPS on.) The difference between sat gps and cellular gps: sat gps uses the gps in your phone to communicate with satellites to get your location. Cellular gps uses your phone service to obtain location information by communicating with cellular towers while you have cell service.

      • I would love to see statistical data on the power consumption of continual GPS power usage and continual cellular coordination power usage. This is something I have wondered about since I first started using a mobile device for navigational assistance.

  4. Did you look into the Miller 102 unprotected battery USB charger?
    https://www.fasttech.com/product/1137904-miller-ml-102-universal-usb-smart-charger-version
    using these unprotected batteries,
    http://www.amazon.com/4pcs-Panasonic-NCR18650B-18650-Battery/dp/B00C26OWGS

    the Miller will charge the batteries and act as a charger, but instead of fixed batteries you have replaceable cells, so you can take as many as you need for the hike you’ll be on, or to get you between recharge points. These are unprotected cells, so you’ll definitely want to buy a battery case to store them in, or some people will rubber band them together and use a ziploc bag.

    Finally, some things not mentioned,
    -The final 20% of battery charge at both ends requires the most time/current to charge. So don’t let your phone drop below 20% before charging it, and don’t waste recharge-battery energy on charging it past 80%. Some argue not to let it drop below 40% before charging it.
    -Temperature has an affect on charge, don’t let the battery get too hot, and don’t let the phone get too cold. Both will cause the battery life to be affected.
    – 100% and 0% as displayed on the phone are not truly 100% or 0%, think of them more as “almost” values. This doesn’t have much real-world meaning, but does have an affect on the internal electronics and battery health.

    Question: what was the supplied current of the DC convertor you used for your charge testing? Most phones can charge on as little as 500ma, but can accept upwards of 2+amps, which can drastically speed up the charge time.

    John Poppe, as for turning your phone off at night vs putting it into a low power drain mode: much depends on your phone, the battery health, phone and battery temperature, and how long you keep it off for. Generally new phones use very little power during their boot process, so if you are keeping it off for 6+ hrs you will use less power shutting it down and booting it up. That said, a physically cold phone and battery will use more power to booth up to warm up the phone. When winter hiking I generally always keep my phone near my body to make sure it does not get too cold, even when sleeping, whether or not I turn the phone on or off. You definitely want to turn off all the antennas and such if you do leave it on overnight. I’ve forgotten/left my phone in my car for multi-day hikes, with it powered up but none of the antennas on, and it only would lose ~4% a day, even in winter.

    • I only tested the RAVPower portable chargers.

      The RAVPower portable chargers were charged using the RAVPower supplied cords and the iPhone 6 plus USB Plug (5W 1 amp). The phones were charged from the RAVPower portable chargers.

      Good points about charging and discharging batteries. One should rarely discharge a battery to 0%.

      I also observed very similar power loss results for leaving a phone in airplane mode.

      Thanks for your post.

  5. I hiked with my iPhone 4s with SIM Lock on which allows you to power on your device and enable the GPS but have WiFi, Bluetooth and Cellular radios turned off. This enabled me to use the GPS function, with maps preloaded, all day. With a 10,000 mAh battery backup, I ended my 8 day trip with 1/3 of the backup battery remaining.

    • I read about the Simlock method as well. I understand that it does not work for the iPhone 5 and 5s. I just conducted a test. I switched off wifi and locked the sim; then put the iPhone into a closed pan and the microwave (creating a Faraday cage). I verified that it had no cellular connection by dialing it. Result: The method does NOT work. The battery was draining at about 5% per hour.

      I hiked the CDT last year using the Guthook app. As an average I consulted the app perhaps every other day. It does not take more than 30 seconds to switch from airplane mode, verify location, and switch back to airplane mode. I never had the battery drained more than 50% after 5 to 8 days of hiking. That drain was mostly for taking photos. I usually started with the phone fully charged and switched off until I took the first picture. Most of the nights I switched off the phone and kept it in the sleeping bag during cold nights.
      I think, if you use GPS as a backup and just for quick verification at trail crossings (to save time studying the map in detail), an iPhone has enough charge for 5 to 8 days of hiking. An iPhone is not the appropriate tool for using constantly as a navigation device. But, as stated already, electronics can fail; so we need paper maps and compass to be sure. The GPS just saves time. You do not have to triangulate your position, which can be hard in woods or flat terrain. And some trail junctions are just hard to figure; GPS is a great help.

      • From what I’ve read this is an AT&T + iPhone 5 specific issue. I’m going to try the Sim lock on my 6 to see if it works.

  6. So, if I’m reading this correctly, there is a power penalty for turning your phone off and then turning it on again, so there is a break-even point for powering down that’s somewhere around 6 hours of downtime. I’m also seeing the suggestion to only charge from external battery when the phone is off. But It also looks like folks are saying that charging over 80% has diminishing returns (wasted energy). If all three of those things are true, and it’s important to mind the charging so it doesn’t go part 80% (so it’s inefficient to charge while sleeping), then is the recommendation to leave your phone off for 6 hours of daylight? What’s the best pattern for use if you were intending on using your phone as an alarm? Part of the thing about bringing a phone is having it available quickly for photography, how does that work if you have to leave it off for more than 6 hours at a time during the day? How do you keep a steady schedule on this stuff? Sounds like a lot of work… ;_;

    • It isn’t a good idea to constantly turn on and off your phone during the day. Doing this 100 times a day would eventually cause damage to the physical switch and drain a lot of power. I suggest leaving the phone in airplane mode during the day so you can easily take pictures and use apps during the day. Leaving the phone in airplane mode during the day would cost you about 3-7% of your battery. This is a minimal expense if you plan on using your phone during the day.

      Charging the last 20% of most batteries takes the most time and is the least efficient. However not fully charging a battery can cause problems with the phone battery life cycle (number of charges a battery can take). Most batteries will last longer if they are fully charged after each discharging cycle. Discharging a battery below 20% is normally not recommended. I recommend following the charging requirements for your specific battery.

      I would only recommend leaving the phone off during the day if you don’t plan on using your phone.

      Turning the phone off at night will save battery life and also prevent your phone from accidentally discharging. If your phone searches for cell reception all night it will most likely drain the entire battery and even the external battery charging the phone.

      If you plan on using your phone as an alarm it would be best to put the phone in airplane mode (or a mode that disables cell service, WiFi etc). This will prevent the phone from accidentally discharging. However if you forget to properly set your phone it will most likely discharge during the night. In this case your alarm will not go off in the morning.

  7. How did you calculate expected battery life for the phones you didn’t directly test? Correct me if I’m wrong, but it looks to me that you simply extrapolated from internal battery capacity in mAh. That’s not going to give an accurate extrapolation, because it doesn’t account for differences in power draw between the devices. The display is the most power-hungry part of any device, and as battery capacity goes down from the 6+ screen size goes down as well.

    • Data was not simply extrapolated from internal battery capacity in mAh. Each phone was analyzed by looking at the individual power draw (mAh per hour) for talk time and standby (airplane mode). The external batteries were also tested to see the actual power transferred to the phone batteries (Samsung S5 and iPhone 6 Plus). Using this data one can easily calculate the days of use of a phone under various conditions.

  8. First of all, thanks for all of the data! Very useful info for those of us that use our phone as a tool on the trail.

    A few more notes on the Samsung Galaxy S3 (which I carry):
    1) Make sure you have Power Saving mode enabled. Power saving mode allows processor clock speed to be automatically reduced when the apps running are not processor intensive. This will save power, especially if you keep the apps running to a minimum. For example, if you use the camera app, stop the camera app when done.
    2) The S3 has a barometric pressure sensor which can be used to get altitude with the proper app installed. I use Baro Altimeter because it is simple and has big fonts which can be easily read with the screened dimmed. As long as I am not lost, I leave the GPS antenna off and get a fix using altitude and a trail profile such as provided in the Guthook apps.
    3) I carry a phone with a replaceable battery to save a few ounces. The S3 batteries are 1.3 oz for 2200mAh.

  9. I find that buy turning off my phone and leaving it in the car the battery lasts a really long time.

  10. I’ve been using a great solar charger for 4 months, the Levin Sol-Wing: http://www.amazon.com/Levin-trade-Sol-Wing-Ultra-slim-Efficiency/dp/B00JKEISBU It costs $45 and weighs 15 oz. and has lots of hanging loops so it’s easy to put on your backpack, a tree, etc. It folds in half to about 12″ X 7″ X 1/2″. It has a pocket which will hold my iPhone 6+ sized phone, regular charger, cables and small external battery. It takes 4 hrs to go from 0 to 100%. It will charge while using the phone, but slower.

  11. The white vs black screen thing is only true for AMOLED screens (Samsung phones, some other android phones) – LCD screens (iPhones, some Android phones) use the same amount of battery no matter the color being displayed (only brightness matters.

    • I quickly looked at the 4s specs and I would estimate that it would perform closely to the iPhone 5. I didn’t run the actual calculations but it should be pretty close.

  12. Great article, thanks much Paul. One very pertinent fact about rechargeable batteries of all chemistries is that they lose capacity (mAh) over time and charge/re-charge cycles. For Li-Ion (used in phones) a fair estimate is that your 1 year old phone, used and re-charged daily, has about 75% of capacity compared to when it was new.

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