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When backpacking, I might carry a MagLite flashlight or something similar that requires two AA batteries. I tend to favor rechargeable batteries for a variety of reasons.

How can I recharge my batteries in the wilderness?

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How long do you plan to be out? LED flashlights are so efficient that a single AAA can go a long time. –  Jay Bazuzi Feb 3 '12 at 18:40
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What are the devices that people use that chew through so many batteries that this becomes an issue? I can't carry more than about a week's worth of food without resupply, and the only gadgets I use (headlamp and GPS) are so energy-efficient that I go through zero batteries in that amount of time. –  Ben Crowell Jul 14 at 0:56
    
Related question: outdoors.stackexchange.com/q/1260/3143 –  Paul Paulsen Jul 22 at 12:09

4 Answers 4

up vote 16 down vote accepted

Perhaps the most obvious and commercially available is solar, which has options ranging from small pocket-sized chargers to roll-out military grade flexible panels. I believe Brunton makes a consumer grade version of the latter (not as bullet-proof), and iGo has some nice versions of the former.

I have used both with some success, the panel is probably over-kill if you are just looking to charge a few AAs (we were charging GPS dataloggers and hand-held computers). However, the small ones are not something I would depend upon, tending to charge slowly. Both require (of course) sunlight.

The second option is to carry more batteries -- either another set or two of fully charged batteries in the size you need, or if you have a variety of other electronics to charge, an old-school camcorder battery can be used to re-charge smaller batteries. Some companies make recharge-able power-packs geared toward cell-phones which function the same way.

However, for anything critical (emergency devices) I would highly recommend ALWAYS packing a set of fresh, regular batteries that you can slip in when your re-charge options fail.

Digression 1: I've often thought a little hydro-generator would be slick if you are camping near a creek - plop it in the current and charge overnight... but have yet to find one (or hear of a do-it-yourself) that is practical.

Digression 2: While poking around for the hydro-power, I found this wind turbine which looks like a fun project... and possible could (should) be modified for water-born deployment. Water always flows.

BONUS PRO-TIP: On cold mornings, gently warming a dying battery (ie in your arm-pit, or in a hot cup of coffee) can sometimes get the reaction going just enough to generate a last gasp of energy. Highly NOT recommended as standard practice due to explosion concerns, but in a life-or-death emergency, it might give you enough juice to make that critical radio call.

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People I've talked to say most solar options are really hard to actually charge things while hiking, is that true? –  Ryley Feb 3 '12 at 20:22
    
They work best with direct consistent sunlight - so while hiking is tough. I've strapped panels to my back-pack with some success - but better if you can charge during a "layover" day. –  LBell Feb 4 '12 at 3:14
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pro-tip: lithium AA/AAA batteries weigh about 35% less than regular alkaline batteries, and usually last longer. Some headlamps warn against using lithium. –  furtive Feb 4 '12 at 3:58
    
+1 @furtive -- I just confirmed lithium are lighter alkaline... great bit of info. –  LBell Feb 4 '12 at 4:17
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The good solar chargers for hiking don't charge your batter with solar. They charge internal batteries then you charge your batteries off of those. This allows you to wear the charger all day without having your device connected to it and then charge your own device off of a very stable current. –  Russell Steen Feb 10 '12 at 19:51

Probably as expected, advice varies wildly depending on whether you're talking about relying on charging the batteries for a life / death situation or it'd just be a "nice to have" if such an option was available.

If it's for emergency purposes then just bring a spare set of batteries - or more specifically, one more set than you calculate you'll ever need. These can be rechargeable as well, but if they are make sure they're relatively new and still hold their charge well (this is especially important because in cold temps rechargeables that are a bit worn out can sometimes fail completely. I've had it happen a couple of times!)

Another option is to take a wind up torch - ok so it's not specifically recharging any old batteries, but it does provide you with a source of power limited only by how much you're willing to turn the thing. They're not that expensive these days either - I remember when they first came out and they cost hundreds... anyway...

In terms of actually constructing a recharging station, the simple way would be to purchase a solar powered battery charger such as this one (I'm aware you can't actually buy it from there anymore but you can see the type I mean!) You could also make something yourself out of solar panels - and equally potentially make something to work with the wind or flowing water.

Unless you're just doing it for fun though I'd be tempted to say don't bother - the size of those contraptions is generally much more than several sets of even D cell batteries, let alone AA, so unless you really don't trust batteries to stay charged or you really rely on going through a heck of a lot of batteries, it's still probably not the most practical option.

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I've tried very hard to keep a charge on a smart phone while on backpacking trips. It was used primarily for recording GPS routes and photos to look at later rather than for anything important. I tried one of these Powerfilm AA Chargers on my pack and it worked very well for charging AA batteries, but didn't get enough power for the smart phone. For medium-length trips (1-2 weeks-ish), you'll probably get more power with less weight and less cost by just carrying extra batteries. Beyond that, solar seems like it might weigh less if you don't draw too much power. Possibly some form of hand crank as an alternative.

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I've used this one successfully to charge an iPhone using Lithium AAs - Tekkeon MP1550 - tekkeon.com/products-tekcharge1550.html - I easily charged the iPhone ~2 times with each set of 2 AA batteries –  Ryley Feb 3 '12 at 20:20

Apart from the often mentioned possibility of bringing enough batteries or buying new ones along the way, I would like to list possibilities for recharging.

As already mentioned by @LBell, there are the following two:

  • Solar:
    Solar panels come in a great variety, allowing to find something for most uses. Some models might be able to charge during the hike (see also this question). Downside: They need sunlight and won´t work well in winter or far north.

  • Wind generators:
    I didn´t know that there already exist camping versions of this, so thanks again for @LBell to the link. Looks rather clumsy, but maybe a cool option for a basecamp. Probably no commercial buyable version available. Relies on wind, so maybe not the best option in the woods.

  • Hydro:
    Pretty much the same as wind, but you need to have a nice stream.

Apart from these, I would like to add some.

  • Fuel cells:
    There are different models available, e.g. from PowerTrekk or Brunton. You need to bring hydrogen fuel or special containers that make it out of water, but don´t have to rely on weather conditions. Probably a rather expensive option, but more reliable than the ones above. Note that fuel cells normally are rather sensitive to temperature changes and mechanical stress, so have a good look at the model you are thinking to buy.

  • Thermal elements:
    Using (waste) heat. Different models are available, like this one included in the bottom of a pot or this one included in a multi-fuel stove.

  • Power packs:
    These are additional battery packs made to recharge your devices. Of course, when they are empty, you can´t refill without another power source. However, might be lighter than carrying spare batteries.

Things to look out for Electronic devices look for very different voltages and powers. Make sure, the charger you´re about to buy fits the thing you want to charge or ask the manufacturer if its supported. Rule of thumb: The voltage the charger can supply needs to be higher than your devices input voltage (somewhere around 4-5V for USB-charging, or around 1.5V per AA-Battery), and the higher the power the faster the charging.
Since most of this technology is quite new, make sure to read some tests or reviews. there are device where a nice idea is behind it but it wouldn´t work too well in real life...

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