HOME

USB power on the trail


Backpacking USB power - what does it take?


I did backpacking as a Boy Scout many years ago and there was no need for battery power for anything except a flashlight. Today there are lots of things which are power hungry. GPS, camera, watch, water filters, satellite communication and even flashlights. But I kept running into the problem of finding the right balance between weight and keeping all my “toys” recharged.


My first attempt used the all-in-one solar power/battery pack to re-charge my iPhone. It lasted about two days (of a 8 day hike). I spent the next hikes refining what I wanted to do and testing different batteries and solar cells. I’m going to share what I learned and how YOU can figure out what YOU need.


The breakthrough was finding a cheap USB device to measure current/voltage and POWER (measured in Amp-Hours or Watt-Hours). I bought from Amazon a USB Safety Tester, Digital Power Meter Tester Multimeter Current and Voltage Monitor. It cost about $11 and well worth it!


The first step in “trail power management” is to understand your on-the-trail power needs. I think it makes sense to use MY requirements to see how I figure it out and you can do the same for your needs.


For serious backpackers the total weight of devices and usability will dictate the appropriate solution for you.


Power Needs


I'm a nerd and really like data.


     1)     I use an iPad Mini for navigation AND to record my hikes’ GPS track (including altitude) as I hike. (FYI I use the apps Motion-X GPS to record tracks and Gaia for navigation/track recording). Most days we are hiking 4-8 hours (once in a while up to 12 hours hiking). My iPad tends to be down 15-30% down from full after a day’s hiking. THIS IS IMPORTANT as my iPad is the most power hungry item in my pack!

     2)     I wear a Garmin Fenix 3 watch and a chest heart rate monitor. I like to look at my wrist to see approximate distance. (The Garmin is TERRIBLE for distance - it is off from 10-40% too high). I use for ascent/descent and heart rate - and as a (wait for it) clock time. After a day it is down 30-60% after a full day hiking.

     3)     I use a mirrorless camera - Fujifilm X-T2. One reason I purchased this camera and dumped the Sony A6000 was that the Fujifilm is so much better at conserving power. Even so it is down about 20% per day for taking a few hundred pictures a day.

     4)     We bring a Satellite text/emergency communication - a Garmin In-Reach - but we only use it once a day for “all OK” message or a real emergency. The power requirement is very low - only about 2-5% per day. Generally we don’t recharge it…

     5)     Other: I bring a Kindle and bluetooth headphones - but I don’t recharge these on the trail. When they die, that’s it!


So how does this convert to how much power? Well I used the USB power meter to measure how much power they need … I decided to use mAH (milliamp hour) as my basis for calculation. (Divide by 1,000 to convert to AH (amp hour).)


I used my iPad Mini and played a movie with the screen full bright over a period of a few hours and eventually drained the battery. Then I used the USB power meter to find out how much power it took to fill the battery.


iPhone X - 2800mAH for full fill

iPad Mini - 4,500mAH (milliamp hours) for full fill

Garmin Fenix 3 - 380mAH for full fill

Fujifilm X-T2 - 2,000mAH for full fill per battery


So for a day I use:

iPad Mini 20% per day or {20% times 4,500mAH} = 900mAH / day

Garmin Fenix 3 50% per day or {50% times 380mAH} = 200mAH / day

Fujifilm X-T2 15% per day or {15% times 2,000mAH} = 300mAH / day


or a total of 1,100mAH to 1,400mAH/day to meet my needs (I generally bring two camera batteries so I don’t recharge the camera on the trail - but I could).


Next is to find what can provide my power on the trail


Power Sources


Basically there are two possible sources of power on the trail: solar panels or batteries.


My trial and error I was able to meet my power needs with a 5W solar panel and a 6,000mAH USB battery - but that was before I actually figured out what I needed and how it worked. BUT I was always worried that I might be bringing too much weight and/or what happens if I can’t get sun to do a recharge?


My experience with solar panels has been very enlightening (sic). A great source of information on buying solar cells can be found at the Wirecutter website. http://thewirecutter.com/reviews/best-portable-solar-battery-pack/ It is worth reading how they test solar cells and what makes a good one.


     1)     While it looks cool to put the solar panel on top of the backpack while hiking, you never get much power. Nothing compared to the time in camp with static aim at the sun. Think 1 hour on the trail might be equivalent to 10 minutes in camp. I don’t have proof of that, but it sure feels like that.

     2)     Not all solar panels are good. Some don’t handle temporary shading (cloud, walking in front, etc) very well and turn off and don’t come back on very fast (if at all). See the Wirecutter reviews.

     3)     Don’t even think about an all-in-one battery/solar cell. I found that the heat of full sun exposure gets everything very HOT and the battery will stop charging. Really stupid design. Just use a wire so you can put the charging item in the shade.

     4)     Batteries are very inefficient so it’s better to directly charge devices from the sun BUT some devices won’t trickle charge (iPad) so it only works when the sun is very bright!

     5)     Solar cells require time at camp to keep checking on them and make sure the sun hasn’t moved behind a tree. Many times I would rather take a nap than babysit a solar cell.


That being said, I have been using the Suntactics 5W solar Cell https://www.suntactics.com/scharger5-portable-solar-charger light weight  and sturdy. (8.7oz) More on weight later.)


While I need to do more testing what I found was I could get 600mAH per hour from my Suntactics 5W solar cell. (Direct sunlight from my porch in Northern California.) Those real nurds will think 5W for an hour should be 5,000mAH, wait something seems wrong here. Well at peak output I have seen the Suntactics create 1A of current (that’s 5W), but it’s rare. Most of the time I see closer to 0.5A of current - still 2,500mAH per hour. I would rather use the measured power to predict what I’m going to need on the trail… specs are wonderful, but not great. BTW I have an older 15W solar panel and it didn’t get much more power than the Suntactics 5W panel (and weighed twice as much).


So if solar was all I had and could directly charge my items it would take about 2 hours per day of bright sunlight to recharge all my devices. (600mAH x 2 = 1,200mAH). If the Suntactics folks write and say that I should be getting much more per hours - they might be right. It doesn’t change my bottom line for what I carry.


Batteries


There has been lots of progress on USB battery packs over the last 3 years. I have a drawer full of batteries, each slightly better than the last - but that was before I got my power meter! (I’ll be buying more batteries!) I have found that I really like a good display of how much power is left and is it charging. None are “perfect,” but much better than the first generation. Once again I look at the Wirecutter (http://thewirecutter.com/reviews/best-usb-battery-packs/) to help understand what is offered in USB batteries - but I care more about capacity than convenience (I don’t like their recommendation for midsize battery since it doesn’t have a good capacity compared to others.)


Lots to learn about batteries - first, don’t believe their rating. MEASURE IT!! I have two batteries I have used before I got the power meter. I tested them and learned a lot.


The rated battery capacity isn’t what you get. Let me focus on the EasyAcc 6,000mAH battery. To fill the battery it took 5,200mAH. So from empty to full took less than spec. But MORE IMPORTANT to power devices from full to empty provided 3,500mAH of power. Wait, I put in 5.2 and got back 3.5 -  67% efficiency! That means if you charge the battery with a solar cell you will need that much EXTRA power to fill it - it’s much more efficient to charge a device directly from the solar cell.


But more importantly, this 6,000mAH battery only provides 3,500mAH of power. Or about 2.5 days of power - not that I would run out of power in 2.5 days, just that my external battery would be empty in 2.5 days. (The wirecutter website shows another battery of similar size that provides twice as much power … I may get one of those.)


So here is a rundown of two of the batteries I have:


EasyAcc 6AH battery (5.3oz)

E->F 5.2AH

F->E 3.5AH


Ravpower 22AH battery (14.6oz)

E->F 20.5AH

F->E 14.6AH


In the future I’ll buy a battery, get it home and measure what it really holds and decide if it’s power to weight ratio to see if it meets my needs - and return it if it doesn’t.


Wires


In addition to the power sources and devices, you need to have wires to connect things together. Some of the batteries have wires built in. I don’t like those. AND not all wires can carry the current (yea, I never believed “Monster Speaker Cable” made any difference, but this time I can MEASURE that some cables just won’t provide full power!)


So I bring two cables and a current meter when I hike. The cables can drive (at full current) my iPad OR my USB-Micro devices.


Not very impressive, but it works!!


Bottom Line


My longest hike tends to be about 8 days. So I could use 11,200mAH of power for the whole week (1,400mAH times 8 days) - and I would still have full power in all my devices when I left the trail. So I have two options: Solar Cell and a small battery OR just the big 22AH battery. Both would work BUT the battery alone is far less hassle! Just be careful on using power. But what about total weight?


Solar cell and small battery 14 oz

or

22AH battery: 14.6 oz (or maybe 12.6oz for the Anker PowerCore 20100mAH battery)


So bottom line I will only bring the 22AH battery PLUS an extra camera battery (they are really light) so I will have plenty of power and none of the solar hassle.


I’m not alone. I follow a hiker “Wired” in her gear journey for long hikes. http://walkingwithwired.com/gear She has gone with the Anker PowerCore 20100mAh 12.6oz “brick.”  I do think we share similar approach to power (although I use lots more in my iPad use).


So you should have enough information to figure out what YOU need and what will meet your needs on the trail.


Would love to hear your comments/suggestions on this.


Jerry

Jerry Pierce

September 18, 2017

Updated December 2017 after getting an iPhone X - that has a great display for bright sunlight and uses far less power than the iPad Mini