Disposable batteries are just not ideal for backpacking. After every trip, batteries keep piling up – whether from headlamps, Steripens, or even just from non-backpacking devices we used around the house. Most of the time, getting back from a trip batteries will still have some juice left, but how much? Enough to take along next time? I found myself either installing new batteries for nearly every trip, or taking extras, unless I’d barely utilized the batteries the last time around. Worst of all, a lot of the batteries weren’t exactly common sizes, so it was impossible to fully use the mostly drained batteries in other devices – not many TV remotes take CR123a batteries. The “need to fully drain” stack of batteries kept growing. That’s when I decided it would be best to move to a standard format. The venerable AA battery. And not just normal batteries, rechargeables.

Now, I’ve had some not so good experiences with rechargeable batteries in the past. Charge them all night and it seemed like they’d only last 10 minutes when used. Worst of all, let them sit fully charged for any length of time, and they’d have barely anything left when needed. Then I heard about the Sanyo Eneloop battery, which maintains 85% of its charge after sitting an entire year. Best of all, the Eneloop can be recharged 1500 times – enough for decades of use for most backpackers (specifications for Eneloop model HR-3UTGA). Sanyo has also developed the newer HR-3UTGB which increases these numbers to 90% and 1800 cycles, but they can be difficult to find and are more expensive. Both models have the same total capacity when fully charged. Once the battery choice had been decided upon and I began to migrate any device I could to the AA standard, a recharging solution was needed, one that would work well both in the field and at home. I needed something reliable, compact, and lightweight.

The PowerFilm USB+AA Charger

PowerFilm Solar manufactures a rather wide array of solar products, but for backpackers who utilize devices that run off AA batteries or can recharge via a USB connection, the PowerFilm USB+AA solar charger stands out. The charger is listed at 4.9 ounces without batteries, but we were surprised to measure an actual weight of 4.6 ounces. Retail price is right around $85. Two Eneloop batteries are included that weigh just under an ounce each (.9 ounces) bringing the total weight to 6.4 ounces. If you only want to recharge using the USB function you can’t leave the batteries at home to save weight – they must be installed, and have some level of charge for charging to work. The unit has 4 flexible solar panels that fold up accordion style, all leading to the plastic battery compartment secured with a hinged clear plastic door. The entire unit is backed with heavy fabric, and when not in use, or when charging via USB, this serves to protect the panels and battery compartment by wrapping around the entire package and securing with a Velcro closure.

4 grommets allow you to fasten the charger to a pack or object for charging. Moving to the outside of the battery compartment, on one side you’ll find the USB charging port, and on the other a simple red LED charging indicator status light. A slow flash means the batteries are charging, a rapid flash indicates an error / incorrect battery polarity, and a solid light is supposed to indicate a full charge (more on that later). The charger is rated to fully charge an empty set of Eneloop batteries in 5 hours of full sun. The charger isn’t waterproof, but PowerFilm states that light moisture can just be wiped off and that if the charger does get soaked, it’s usually not a problem as long as you remove the batteries and allow for a full drying. However, solar charging in the rain probably won’t work out great anyway. I'd suggest storing the charger in something like a Sea to Summit Ultra-Sil dry bag when not in use. Overall the charger feels quite solid for such a lightweight package, and is small enough to fit in a large pocket.

Performance

Curious to see how the charger performed, I hooked up an iPhone 5 to the device and charged the phone until it stopped charging, then ran each battery through a headlamp to make sure the batteries were fully discharged. After unfolding the unit, I aimed it at the sun and continued to track the sun’s movement over the next 5 hours. I then folded up the unit so it wasn’t receiving any additional juice from the sun. After completely running the battery of my phone down and plugging into the PowerFilm’s USB port, it was able to raise the charge level of my phone from completely dead to 37%. I repeated the test over several more days and weeks, and consistently was able to raise the charge level of my phone about 40%, with a maximum of 45% in a single test after charging in full sun for 5 hours. All testing was performed with the iPhone’s radios disabled, applications shut down, and screen off just to level the playing field. I also tried recharging the batteries from an actual Eneloop brand charger from a standard wall socket, which was able to charge the batteries a bit better – enough for a 60% phone battery level bonus.

Obviously, there’s only so much energy that the batteries can hold and they’re not capable of fully recharging the phone. It would have been nice if the PowerFilm charger was able to charge the batteries to their full potential (leaving the charger in the sun for longer periods of time did not result in any additional charge), but it gets close enough to keep you running in the field. One of the nice things is that you can charge the AA batteries by day, then recharge whatever you need to recharge via USB at night. Or of course if you just need the batteries for a device that runs off AA’s, charge the batteries in the sun, then swap into your device. If you need more USB boost than the fully charged batteries can provide alone, leave the solar panels in the sun as you recharge your device via USB. The batteries will drain faster than they charge, but this method will help you get just a tad more charge on your device. Using the iPhone 5, this method allowed for a charge all the way from 0 up to 60%, compared to the usual 40% assuming you started with fully charged batteries.

Disappointingly, you’re unable to charge a single AA battery with charger and I found that working in pairs was required…you’ll get a battery fault if you only insert a single battery, and when I tried to mix discharged batteries with fully charged batteries, the uncharged battery would not charge in the sun. I can only assume this is to prevent overcharging of the already charged single battery. With this in mind, I’d actually have to take an additional rechargeable battery along for my headlamp that takes a single AA, then run both batteries down before I could recharge them together. For full performance, I suggest always working with pairs of batteries that have an equal charge. If you only need to recharge devices via USB, this isn’t a concern.

Durability of the product hasn’t been an issue, it’s solidly built. The weak point in the armor however is the face of the 4 solar panels themselves – use caution when charging as they do scuff and scratch rather easily.

Some care is required with the face of the cells, as they do scratch easily.

LED Indicator

Immediately after you unfold the panels and expose them to light, the red LED light will begin to flash to indicate charging. You’ll get the rapid pulse if you’ve inserted the batteries incorrectly, but a few times I’ve received the rapid pulse for no apparent reason. Folding the panels to shield them from light and then unfolding usually resolved the issue. If that didn’t work, removing and reinserting the batteries as required. What doesn’t work so well is the full charge indication. The red light will turn solid well before the batteries are fully charged. PowerFilm states that the light actually turns solid at a 75% charge level and advises to charge by time to remedy the issue, but in my case, I generally received a solid red light after about an hour – good for just a 10% boost on the iPhone 5. If you’d like to charge the batteries as much as possible, just leave the unit in full sun and check your watch, as long as you’re aimed at the sun or close to it, you should have a full charge in 5 hours.

In sunlight when you'll be using the PowerFilm USB+AA, it can at times be difficult to tell if the red LED is illuminated.

Performance 2

Solar panels definitely work best in a base camp type situation, where you monitor the panels to ensure they’re in full sun and aimed properly during the charging process. But I also tested the PowerFilm during a less than ideal scenario while on the move during a recent weekend trip. Strapped to the outside of a pack while hiking, the panels will very rarely be at the optimum charging angle. The day started with two completely discharged batteries inside the PowerFilm unit and a sunny day. I gave the charger a head start by facing it directly at the morning sun as I worked to break camp for 30 minutes, the shouldered my pack and hit the trail.

By lunch time a thin haze blanketed the sky, and I gave the charger another 30 minutes pointed right at the sun while I ate lunch. As I hiked after lunch the haze thickened and it became completely overcast for a couple hours, however by late afternoon the clouds rolled out and it was once again a sunny day. The charger was simply strapped to the top of my pack as I hiked through a mix of wide open spaces with more light as well as shadier aspen groves, though the trees were without leaves for winter so there was a mix of sun and shade. After 10 hours of hiking, I gave the hopefully charged batteries a shot. They were fully charged and added a 43% charge to my phone. So even in less than perfect conditions the charger worked over a day’s worth of hiking, though experiences will of course vary based upon the length of the day, tree and cloud cover, and direction of travel.

The PowerFilm USB+AA packs into a very convenient and packable form factor.

Conclusion

The PowerFilm USB+AA charger is a great fit for lightweight backpackers who need a solution to charge devices in the field – as long as those devices will take rechargeable AA batteries or can recharge via a USB cable. On shorter trips, or if you’re not a heavy electronics user it will probably be lighter and more efficient to simply take spare batteries instead, but if you’re planning extended jaunts or utilize power hungry devices like a GPS frequently, the PowerFilm charger might end up making things easier. The charger isn’t without its quirks, and we found ourselves wishing for an accurate full charge indicator and the ability to work with a single AA battery instead of in pairs. However, the unit is quite light, the price is manageable and best of all you’ll get a single, compact unit that almost does it all.

You can find the PowerFilm USB+AA lightweight solar charger here at Amazon.com for about $85. For other solar charging options, you can check out our Solarpad Pro solar charger review as well as our Lixada 10 Watt solar panel review.

Editor's Note: This review originally appeared in Issue 7 of TrailGroove Magazine. You can read the original article here for additional photos, pros and cons, and our rating of the PowerFilm USB+AA solar charger.