A Few Notes on Solar and Portable Chargers for Backpacking

Let’s talk about keeping your phone and devices powered while not being tethered by an extension cord of epic lengths. While out shopping, here are some of the terms you’re going to need know. Pay attention there is some math involved and yes there is a test at the end!! Don’t worry, there are some pretty pictures too.

For batteries and USB devices, we are going to need Voltage, Current, and Power. We are also going to need their units of measure; Volts, Amperes, and Watts. For solar chargers, we are going to need a few more. I’m going to admit here and now that the solar stuff is new to me so if you’re more techno weenie than I am and I’ve screwed it up, please let me know. For solar, we need the type of cell; CIGS or monocrystalline and solar cell efficiency. From all this gibberish, we are going to derive even more.

Depending on the marketing department or the direction of the wind, you may see Voltage, Current or Power on the USB packaging. There’s no requirement for them to be clear, concise, or even correct. The one fixed value in all of this is that anything USB is going to be 5 VDC (Volts Direct Current). When looking for a USB charger (be it for the car or the wall), you want the highest rated in Amps or Watts***(see below). Because the voltage is fixed at 5 VDC, you can compare Amp to Watts with simple multiplication table from 3rd grade. If your package says 15 Watts, it’s a 3 Amp charger (15w ÷ 5v = 3a). If it’s 2 Amp, it’s 10 Watts (2a x 5v = 10w). If the package reads 5 Watts or ½ Amp, it’s complete garbage. Set it down, walk away, pretend it never happened.

Voltage = Volts = 5 volts
Current = Amperes, Amp, A
Power = Watts
Chargers = Ampere Hours = uAH (milli amp hours)
Ohm’s Law is P =E * I where P = Power (Watts), E (or V) = Voltage (Volts), I = Current (Amps)

Ohm's Law

Handy dandy Ohm’s Law wheel; set that Best Buy kid straight. You’ve got this!!

Batteries, be they in your phone, in your charger, or in your pacemaker, they will be rated in Ampere-Hours.

The charger I bought (https://powercartel.com/teardowns/tomo-v8-4-soshine-e3-diy-usb-power-bank-teardown/) takes 4 batteries. There is also a 2 battery version available. It uses the 18650 cell. It’s about the size of the battery if a D cell and a AA cell had a love child. The secret decoder ring for the lithium-ion battery (the same kind in your laptop battery) sizes is XX-YY-0. So my 18650s are 18mm x 65mm. For comparison, the AA cell is 14.5mm x 50.5mm. There are exceptions but the general rule of thumb is the bigger the battery the bigger its capacity (in Amp-Hours), the longer it lasts.

The Wiki says …
“An ampere-hour or amp-hour (SI symbol A·h or A h; also denoted Ah) is a unit of electric charge, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3600 coulombs.”

And then it continues to ramble on in techno geek weenie stuff. The short version; The bigger the number the better. But there’s a catch. People are greedy and lie. There are internet listings for the 18650 battery as high as 5,000 mAh each. That’s a complete and utter lie. 3,000 mAh is about the best you can get at this time. Panasonic is one of the top brands and one to go with.

Tomo V8-4, shipping weight 3.81 oz (w/o batteries), batteries 1.57 oz each

Tomo V8-4, shipping weight 7 oz (w/o batteries), batteries 1.57 oz each

Anker 2nd Gen Astro E5 16000mAh External Battery

Anker 2nd Gen Astro E5 16000mAh External Battery, weighs 10.88 oz

One popular model portable charger is the Anker 2nd Gen Astro E5 16000mAH External Battery. Looks good on paper but I wasn’t able to find anything on the batteries they use. It weighs 10.88 oz and at 16,000 mAH it has more charge than mine (12,000 mAh & 10.09 oz). The Astro also has a flashlight which may be useful in its own right. The big plus is that it will put out 3 Amps in a single USB port. Mine does 1 Amp and 2 Amps depending on port for a total of 3 Amps. This is something that tricks the unwary consumer. ***(Trick question from above) Total power is NOT always the same as the power output of a single port. For the Apple users out there, this is good as Apples can get picky about their power sources (they like 3amps). I am however a little suspicious as to how Anker’s do it while being roughly the same weight. So, if you have one and wouldn’t mind busting it open … let me know what it has for batteries.

Solar chargers … this is uncharted territory for me. Aside from my Casio calculator from 9th grade (damn fine calculator that still works to this day and does fractions), I don’t have much experience with them. So, off to the interwebbernetz again. One term that sounds important is Solar Cell Efficiency.

Solar Cell Efficiency is the ratio of the electrical output of a solar cell to the incident energy in the form of sunlight. The energy conversion efficiency of a solar cell is the percentage of the solar energy to which the cell is exposed that is converted into electrical energy. ~ so sayth the mighty Wiki.

Gear Review: Apollo 6 Mobility Package Solar Charger and USB Power Pack

Gear Review: Apollo 6 Mobility Package Solar Charger and USB Power Pack

Sprinkles reviewed the Apollo (https://thetrek.co/apollosolarcharger/). It was rated at 15%. Sounds pretty low to me but again I’ve no clue. Turns out the record was just broken by Panasonic at 22.5%. And they can’t even hit that number in production run quantities.

There are two types of solar cells out there; CIGS (copper indium gallium selenide) and monocrystalline. More fancy talk. The CIGS are flexible and roll up. Sprinkles’ is a CIGS. The moncrystalline are the ones you see on the roof tops. Not exactly something you want to trot around with in the woods. Now there are some mono’s that fold and are packable. Here’s a random one that I found on Amazon.

Mercury 10 Solar Panel Portable Solar Panel Charger

Mercury 10 Solar Panel Portable Solar Panel Charger

It puts out twice the power at a third of the cost of the one Sprinkles posted but it comes at a price; it’s three times as heavy. Hers is 6 oz and this puppy is 18 oz. Now, before you jump at the Amazon one or the one Sprinkles posted consider this…

The question asked eleventy bajillion times “Should I take a solar charger on the A.T.?” Here’s some more wiki:

By convention, solar cell efficiencies are measured under standard test conditions (STC) unless stated otherwise. STC specifies a temperature of 25 °C and an irradiance (G) of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. These conditions correspond to a clear day with sunlight incident upon a sun-facing 37°-tilted surface with the sun at an angle of 41.81° above the horizon. This represents solar noon near the spring and autumn equinoxes in the continental United States with surface of the cell aimed directly at the sun. Under these test conditions a solar cell of 20% efficiency with a 100 cm2 ( (10 cm)2 ) surface area would produce 2.0 W.

How often does this happen on the East Coast much less in the A.T.’s “Green Tunnel”? The formulas for Air Mass and Solar Cell Efficiency start looking like a nightmare designed by Einstein when you change elevation, temperature, atmospherics, etc. The higher air mass in the Rockies is reduced by the atmosphere attenuation (junk including water vapor that’s floating in the air), temperature inversion, … MAKE IT STOP!!

Bright sunny day

Bright sunny day

On a perfect day without a cloud in the sky on a low humidity day standing on a mountain bald, bust out your solar charger!! Using the Anker battery pack and Sprinkles’ solar charger (paper numbers), you are going to need about 16 to 18 hours of those conditions to get a full charge. If all you’re trying to do is charge your phone enough to call the paramedics after a stalking bear caught up with you … it won’t take 16 hrs. If you’re hiking the PCT or the CDT and the last time you saw tree or cloud was 3 days ago, maybe a solar charger is worth the weight (your decision, HYOH). Don’t let anyone stop you if you’re inclined to carry a solar charger and the techno stuff the Professor on Gillian’s Island could only dream about. If you’re going au natural with the bowie knife then you didn’t need to read this. Good luck to you brother (leave bail money with a trusted friend).

Regardless of solar charger, battery pack, or even wall chargers you should field test your equipment for at least a rough guess of charge time. You may get a full charge while doing the half gallon challenge or you may roll out of the hostel the next morning with a 50% charge. As my phone is good for about 3 days in airplane mode and I get 3 charges off my battery pack (your results WILL vary), I’ll see you in town about every 9 days I guess.

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Comments 4

  • Colleen Goldhorn : Nov 10th

    I own the Anker mentioned above, and I would highly recommend it. It’s a really great charger, and fully charges my Samsung Galaxy s5 about seven times. The only down side is that it takes 8+ hours for the Anker to fully charge. Other than that, great battery option!

  • Connor Carter : Apr 10th

    At the least it’s more informative than one of those reality TV stars,
    kim this? Joey what?

  • Backpacking Enthusiast : Jun 7th

    Great information about solar charging! I think a solar charger is essential for backpacking! You may need help or just need to check in with family and friends. People need to know your general proximity in case of an emergency. Thanks for this very helpful information! Keep up the good work! Backpacking Enthusiast

  • Hiking Grandma : Jul 12th

    I enjoyed your article about charging with solar! We love this, wonder what we ever did without it. We love the outdoors, my husband and I, but we are not hot not cold weather hikers/campers, fair weather is the game for us! We have been using solar devices and love it because of the fact that you can stay connected with people, good for GPS, and good in case of emergencies. Solar devices are amazing, and the only way to go! hiking grandma


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