Ruck Sack Battery Charging System

Posted: 02/26/2016 in Communications

A reader recently requested I elaborate on the comms equipment battery charging system I carry in my Ruck.

First let me say that the setup I use is not what I would prefer but it works. I would prefer an ultra light weight system that I could attach directly to my Elecraft KX3 and charge the batteries using its built-in battery charger. The radios built in charger requires 13.8 volts dc but I haven’t found a pack-able panel that supplies that voltage. Most backpack/camping panels supply 5 vdc. That would require 3 sets of panels connected in series to get the necessary voltage. So, what I’ve had to resort to is removing the batteries from whatever radio I’m using, and charging the batteries in a charger that’s connected to the solar panels.

My current setup consists of the XTAR VC4 Charger and the Renogy Solar 14 watt E-Flex Solar Power Panel with dual USB ports.

I chose the XTAR based on its light weight and size, its ability to recognize and charge 4 different batteries at once and charge a wide range of Li-ion, Ni-MH and Ni-Cd batteries, plus pretty good Amazon reviews. So far its performance has been good. On the downside, it’s not waterproof,  but then I haven’t found one in its class that is. And while it’s not fragile, it’s not private-proof and should be packed in  your ruck accordingly. Last but not least, you have to use the XTAR provided USB to charger cable. Why they didn’t design it to accept a common double sided USB cable or micro to USB cable is beyond me. So until I can find a spare or make my own, I have 1 cable and no spare. That makes it a critical failure point. The old “2 is 1 and 1 is none….”.

I chose the Renogy 14 watt E-Flex solar panel due to the fact that the solar panels I installed with my home system were also purchased from Renogy and I have been pleased with them. They offered the E-Flex as a camping solar system and I thought for the low price, I’d give it a try.

The E-Flex weighs in at 1.3 lbs, folds up small, has dual USB charging ports and a pretty nifty charge indicator that glows brighter as the suns intensity increases. One downside is the flimsy attaching loops arranged around the perimeter of the assembly. Other manufactures offer heavy duty grommets that can be used for attaching points. Another is the small storage pocket does not seal completely, so be cautious what you store in it.

Charging time for 4 – Panasonic 2500 mAh Eneloop Pros runs about 6 hours depending on the available sunlight and angle.  Charging time for 4 – 2000 mAh Eneloop standards is about 4 hours.

Now you have to ask yourself, which is lighter and takes up less room in the ruck?  Lots of spare batteries or a few spares and the recharging system?  I would say that’s METT-TC dependent.

What is the Mission? Is it short enough that I can just take some extra batteries? Or is it a long term affair where the weight of the recharge gear will be less than the weight of the batteries. Will we be using vehicles instead of walking? Then we just use our cigarette lighter plug-in inverter and charger.

Terrain: If it is a long term affair, what will the weather be like? Cloudy weather would preclude using the solar panel. Will I have the opportunity to lay out a panel for a few hours during the day or will we be constantly on the move? Is the terrain heavily forested?

Troops: Am I or someone on my team in good enough physical shape to hump the extra weight over rough terrain? Do I have the space in my ruck?

Civilians: Are they on our side? Will we be operating in a non-permissive environment where laying out a panel might draw the interest of a civilian who then compromise our location?

I know, I left out Enemy and Time. You get the gist.



  1. mtnforge says:

    Dan, you would really appreciate this book:

    The True History of the American Revolution

    Your great name sake in it, an accounting of Dan Morgan’s part in the revolutionary war like, in particular his leadership during the Patriot offensive against the British in Quebec.
    Aside from that this book is a total gem, I’ve never read anything like it. It is only 99 cents for the Kindle copy. There is so much about the Patriot insurgency and guerrilla war against the English it is a mind blower. I’m not embellishing or exaggerating, you have to read this book. The guy who wrote it obviously made it a lob or of devotion and love, and he has this rather unbiased style that provides a unique insight into everyone on all sides involved and the causes and reasons. Meticulously researched and written. It examines the actions of resistance and winning unique among any history of America I’ve ever read. How this is such an obscure work is beyond me. One thing for sure it answers many questions and misunderstandings about our founding and liberty and why and how it was fought for. Can not recommend it enough.

  2. danmorgan76 says:

    Thanks for the recommendation. I’ve ordered the hard copy to pass around and the kindle to start on tonight based on the info you left over at WRSA.

  3. AC says:

    Bioenno Power has their BSP28 – 15v nominal folding solar panel.
    Amazon has a bunch of nominally 18v folding panels. Read their reviews before buying one. Some of them suck.

    Drok makes an assortment of relatively inexpensive up and down voltage converters. You could try one of their boost converters to turn USB 5v out to 13.8v if you wanted to – getting enough amperage out of the panel might be an issue. Alternatively, a down converter can turn 18v into 13.8v from a higher voltage panel.

    A company called PortaPow has a smart USB AA/AAA NiMH charger. I have two of these, but haven’t had them very long. They use a weird male-male USB connector cable.

    The only thing I would say about the folding solar panels is that their claimed wattage is usually *wildly* optimistic. Realistically, you’ll likely get half the watts the product claims out of it, at best.

    • danmorgan76 says:

      AC, thanks for the information.

      I did consider the BSP28 but at 3.4 lbs I had to defer to the 1.3 lb. Renogy. As you know, you don’t get something for nothing and that definitely holds true with solar panels. You want more power, it’s gonna be bigger. I will probably snag one just to play with. Maybe I could sneak it into one of my team mates ruck. I could tell you some stories.

      I looked at the Droks extensively when I started this project but kept smacking up against that pesky Ohm’s law. Voltage up = current down. For a voltage boost of 2.75 times I ended up with .9amps current. Charge times were way too long.

      I have one of the Portapow intelligent USB chargers. It is much smaller and lighter than the XTAR, however, it will only charge AA/AAA batteries. We have some unusual size batteries for various devices; flashlights, optics, NODS etc, that the XTAR will charge. Which charger I would take would be mission/equipment dependent. (There’s that METT-TC thing again).

  4. Wynn says:

    What about a combination of a higher output solar panel and a charge controller that would knock down the power down to something the radio could use?

    and this

    I realize the Panels are 3.4 Lbs and being former Infantry I realize that pounds = pain… but having the ability to get 12v would be helpful… Just a thought. Also if you have something like a laptop to do digital modes you could use it for that too…

    I am a General class Ham and portable ops is something I have interest in…


    • danmorgan76 says:

      Wow, that thing is a hoss! According to their info. it actually weighs in at 4lbs. But again, it is what it is when using solar. You want more power, your gonna have more weight. The price point is good. I guess it depends on what your definition of “portable” is. If you are not carrying much in your ruck it’d be okay. If you’ve got a full load out…

      • Wynn says:

        Yea….like you said… METT-TC rules apply….

        I mean if you want to really light get a mountain topper with a 9 volt battery.. LOL… But That does me no good since I don’t know cw…

        I wish I could afford the KX 3 but will have to live with my 857D… Hence the reason I would need more power… 🙂

        Great article BTW…

  5. FrozenPatriot says:

    Consider this as a solution to your voltage problem:

    Quality might not be the highest, but it just may be good enough. If you think something like this in a higher quality or higher power version might sell, contact me and I can build you one.

    • danmorgan76 says:

      Thanks for the comment. The device looks interesting for a lot of uses. I’d say someone has managed to cable a Drok. Again the issue is when you boost the voltage you drop the current. Hard to get around the math.

    • Chris says:

      The PWM solar charge controller is for charging a battery – not for running a radio. If the panel has 18V out, then the output of the charge controller is pulses of 18V, which can destroy many 12V radios. And DC-DC converters will likely generate RF hash. So keep in mind, the likely use of solar panels is to charge batteries, not to power radios directly.

  6. Zulu94 says:

    I use a Power Film thin roll up 28 watt solar panel that is good for wet and dry weather. These panels put out 15.4 volts. They are very light weight. I have a LiFe Po4 battery and a small charge controller that I can bring along for extra capacity. My radio i a a Yaesu FT-857D which is VHF/UHF/HF all in one radio that weighs 5 pounds. Output watts for HF can be adjusted up to 100 watts or down to 1 watt.,6580

    • danmorgan76 says:

      Zulu, Are you charging the internal batteries with your solar panel or are you charging the LiFe and then using it to charge the internal batteries. At 1.9 amps output, how long are your charge times? Also, are you using the charge controller to charge your LiFe with?

  7. gamegetterII says:

    Reblogged this on Starvin Larry and commented:
    Read and figure out how to apply to your gear.
    Be sure to read the comments too-for some additional info/ideas

  8. mtnforge says:

    I used build and race super light wieght grand prix motorcycles, every ounce saved was a great advantage, I even designed fabricated and raced a series of Titanuim chassis bikes. The entire frame, swing arm, and seat subframe weighed 14lbs. So you can see I was very serious about shaving every lb possible. Just the titanium chassis reduced my previous setup by 110lbs gross, a huge increase in acceleration, braking time, and improved handling. Being I was a privateer racer, I had to come up with ways to reduce weight that where cheap. One thing was running a total loss ignition system, as getting rid of the weight and rotational engine drag/HP loss of an engine driven charging system saved 15lbs, and unleashed 7hp for the rear wheel. My ignition used 3-4 amps depending on rpm, found a battery that worked well, a Yuasa hydrogen recycling battery, can be run in any position, weighed 6lbs, having a 6 amp hr capacity at a 10 hr rate, lead wet acid cell construction, Yuasa made it specifically for total loss systems, it has deep cycle characteristics, very high quality components. They make they make a 2.3 hr @ 10hr rate weighs 2.3 lbs, and a 3 and 4hr version weighing 3 and 4 lbs respectively. Good batteries, they take a licking and a lot of abuse on a race bike, crashes, poor charging discipline, engine vibration and high heat. Still it was weight I needed to reduce. I tried power tool batteries, they work pretty good for the weight, but when they reach their cutoff valve voltage, it really cuts off! Like from 10.5 vdc to nothing in an instant. And my engine would quit right on the last lap if I didn’t charge them to the max, and memory problems too, but man they are light weight. With the lead acid batteries, I had one of those little emergency jumper/booster packs I would use to quick charge the lead acid battery between practice rounds, I’m sitting there with a volt meter watching my battery charge one day, and it dawns on me, how about the battery in the jumper pack!!!? That might make a dandy light weight battery. I grabbed a swazall from the truck and cut the guts out of that jumper pack on the spot, inside they have what looked like a capacitor battery and associated charge controller voltage controller inside. A racing buddy came over, pretty smart guy, electrical/mechanical engineer, we cobbled together a battery rig for my bike, and that little battery had similar capacity weighing only 1.5lbs to the 7.5 lb Yuasa lead acid cell. I got the jumper packs at a Northern Hydraulics’ store. They cost about 75 bucks at the time, back in 2002. You get the battery, charge controller. jumpers, lots of nifty bits and pieces you can repurpose, and the case can be easily modified to house your charger section. Another aspect is you can charge off mains power or a 12 volt system. I don’t know the capacity of the jumper pack battery, or exactly what kind of device the battery is, but they worked great, saved a ton of weight, and had the same depth of draw or better as the Yuasa 7lb 6hr capacity lead acid battery for the use i put it to. I’m no electronic guy, I’m a metal guy, but those puppies did the job, maybe you guys can figure it out way better than me. They sure where light. If I remember right, I even saved a bit more weight by making a lighter weight case verses the factory one the capacitor battery came in. I think it was 1.4lbs with 8ga jumpers and quick disconnects. The capacitor battery is tiny, looks like you could never get that much power out of one. But they got something in them, because you can put enough current back in a 12 volt vehicle battery to start a V8 engined vehicle with one, a few times without needing to recharge.
    What I did is a truly improvised power source, cheap and rugged. What the actual capacity is, is for somebody else to determine, but it worked slick as can be, and was 100% reliable for my needs. And for the $75 bucks, it was an easy risk to take, ended up a bargain.
    Think outside the box, improvise improvise improvise.

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