Helping folks get the most out of their electrons while on trail.

Best Practices

Leave phone in Airplane Mode whenever possible. iOS and Android can both use GPS with Airplane Mode turned on. No need to turn Airplane Mode off to use Halfmile/Guthook/etc. Turn phone off overnight or keep it in Airplane mode in a pocket on your body where it can stay warm. Have phone screen turned off whenever possible. OK to leave phone locked but powered on throughout the day. The screen turned on is the #1 power drain on your phone. Never charge or discharge a phone or external battery when the phone or battery is cold. Always warm the phone or external battery in your clothes before turning the phone on or charging phone from external battery. Every evening recharge your phone to 100% from your external battery. The idea is to not let your phone drop below about 80% during the day and charge it back to near 100% every evening. This is one of the most inportant parts of using your external battery efficiently. See below for more notes. Connect your phone to cell service at least every week if possible for best GPS performance (phone will find you faster, so you don’t have to have it on as long, saving battery). See below for more notes.

Example Scenario

You wake up in the morning on trail and pull out your phone (which has been turned off overnight) and put it in a warm pocket near your body so the phone can warm up to near your body temperature before you turn it on for the day. You pack up your quilt and roll up your pad with your phone still turned off but warming up near your body. As you walk away from where you camped, you see a beautiful sunrise and now that your phone has warmed up to about body temp your go ahead and turn it on so you can snap a photo of the sunrise. After taking a stunning photo, you double check that your phone is still in Airplane Mode from the day before then lock the screen and put your phone back in a pocket where it will stay around body temp. Throughout the day you take your phone out here and there to snap photos, check Halfmile, etc- always minimizing the time the screen is turned on. In the evening you reach a high point and can see some cell towers off in the distance, you’ve been wanting to send your husband a message about including some new socks in one of your resupply boxes so you turn Airplane Mode OFF and your phone connects to the cell tower you’re looking at. You send your message, wait a few seconds, then turn Airplane Mode back ON and continue on down the trail. When you get tired and want to sleep for the night, your realize your phone says it has 85% battery. You pull out your external battery (which is around body temp since it’s warmed up through the day) and plug in your phone taking the phone back to 100% charge. You remember reading some article online that said never let your phone battery drop below 80% until your external battery is dead and thank them silently for helping you use your phone in the backcountry for weeks on end. ;)

Suggested set up

Phone of your choice (whatever you already have) Anker PowerCore+Mini 3350 ($10, 3oz) Aukey dual USB (12w) wall adapter ($8, 1.6oz) USB cable to charge your phone (you already have), USB cable to charge the external battery (included with the battery).

Advanced set up (for fancy headlamps)

Need more battery capacity?

Notes

Why not allow phone to drop below 80% before recharge from external battery?

Most phones will charge at a very fast rate up to 80%, then slow down the rate at which they charge from 80% to 100%. Many folks have heard they should keep their phones below 80% (like between 40% and 80%) to take advantage of the fast charging from external batteries. Although charging your phone from 40–80% will be faster than keeping it above 80%, the high draw/charging rates from your external battery to the phone are much less efficient than charging in the slower zone (80–100%). On trail we’re not concerned with saving 10 minutes to charge our phones as fast as possible, we want to squeeze every last electron out of that external battery pack and transfer it as efficiently as possible to the phone. You may notice when charging your phone quickly (below 80%) there is heat generated both in your external battery and your phone. This heat is wasted energy (a lot of it). By slowing down the charging process, less heat is generated, and more juice gets from the external battery into the phone.

Why use a big heavy 18650 headlamp?

Using a headlamp that takes 18650 size rechargable batteries along with the F1 charger allows you to decide which is more important to you in a section of trail: more headlamp use, or more phone recharging. The suggested LG INR18650MJ1 batteries each have a capacity of 3500 mAh, each more than the Anker mini external battery. You also don’t have to carry spare headlamp batteries since your ‘phone’ 18650 can be used for headlamp if you need it.

Why connect phone to cellular every week?

Your phone uses a baby GPS that needs to get updates about messed up satellite orbits and timing adjustments. With a normal GPS reciever this is downloaded from the GPS satellites themselves (takes about 15 minutes), but phones get this data (the GPS Almanac) from a cellular data connection. Some phones (iPhone) can get this data from Wifi too, unsure if Android phones can. When the GPS Almanac is more than a week or so out of date your phone will have issues finding you quickly or reliably.