I started looking for a battery-powered smart phone charger, and the search has turned out a bit harder than I thought. Regular (dumb?) phones don't demand as much power, and can be charged with a AA battery. I think smart phones need more. I found some candidates on Amazon, but nothing with rapturous reviews. In fact, the brand I used to use seems to have fallen down flat on its face. Any recommendations? Thanks!

Bingley

EDIT. Forgot to mention that this is meant to be an emergency charger for a common battery size (like AA or AAA). Small size and portability are important for this purpose.

I have had good luck with the Energizer XP2000, though I don't know if you're looking for a charger that will run on disposable cells. The XP2000 is a lithium polymer design that holds a charge well. You recharge it from various sources.

The cables & tips provided are a bit chintzy, but I don't use them. My Moto Droid 2 phone came with a great charging cord that has micro-USB on the phone end and 120VAC prongs on the wall end, but the 120VAC prongs pull off to reveal a standard size USB connector. So with one cord I can charge the phone from the wall, any powered 5VDC USB outlet, or the XP2000. Then later I can re-charge the XP2000 from the wall or any 5VDC USB outlet.

I have a micro-to-mini USB adapter that I tethered to the same cable that lets me connect a USB-powered external hard drive to a computer. It sounds trivial but it really helps cut down on the cable tangle in my EDC bag.

I've been using one of these for my Samsung B2710 handset and to power the portable stereo Bluetooth speaker system

;

http://www.amazon.co.uk/TeckNet-Dual-Port-Universal-Incredible-Blackberry/dp/B000NDQ92W

The twin USB outputs are really handy, but you would need a Mains to USB PSU to charge the TeckNet Dual-Port iEP380 5000mAh 1.5Amp Output Universal USB Battery Pack.

http://www.amazon.com/New-Trent-iDual-Port-IMP50D-Blackberry/dp/B003690Q42

The New Trent iDual-Port Pack IMP50D 5000mAh External Battery Pack available in the US is basically identical.

There are a bunch out there. I've got one for my iPhone that works well, but it doesn't seem to be made any more.

Bingley,

If you have minimal skill with a soldering iron or are open to building a new skill take a look at the MintyBoost from limor fried. It will charge most any smart phone of device that can be charged from the USB port of a computer.

The following is from the device web page. I can not recommend the device enough. There is even a solar version on the site.

Learn to Hack, Hack to Live,
Jim

(Hack as in A clever or elegant technical accomplishment)

http://www.ladyada.net/make/mintyboost/

Minty Boost: Portable USB power

Overview
This project details a small & simple, but very powerful USB charger for your mp3 player, camera, cell phone, and just about any other gadget you can plug into a USB port to charge! (See below for compatibility tests)

The charger circuitry and 2 AA batteries fit into an Altoids gum tin, and will run your iPod for hours! 2.5x more than you'd get from a 9V USB charger! (See Process for math/calculations) You can use rechargable batteries too.

Specifications:

Version 3 now works with iPhones and newer iGadgets!
5V output @ 500mA output
Fits in your pocket
Recharges just about any gadget with a USB cable
Uses any AA batteries!
Upgrade to C or D cells for a mega battery pack

Some numbers...

iPhone (all types): 3/4 full recharge
iPod video (tested, using alkaline batteries): 3hrs more video (1 full recharge)
iPod mini (tested w/rechargables): 26 hours more (1.5 full recharges)
iPod nano: 4 full recharges!
iPod shuffle : 60 hours more , 5 full recharges!

This project is suitable for beginners, some soldering tools are necessary but even if you've never soldered before it should be pretty easy. You can etch a circuitboard and/or breadboard this up, or simply buy a kit from the webshop.

To charge a iPhone4 the battery requires approx 5.3 Whrs ( Built-in rechargeable Li-ion battery 3.7 V at 1420 mAh ) with a charge efficiency of say 90% and a DC-DC converter efficiency of approx 70% you are going to need around 7-8 Whrs of AA cells i.e around 4 Hi capacity NiMh AAs or around 6-8 Alkaline AAs (for the same charge time). Neither are lightweight or small compared to the dedicated Lithium Ion rechargeable smart phone rechargers.

http://www.amazon.com/Tekkeon-TekCharge-Mobile-Battery-Charger/dp/B0014KLX9C

Perhaps the Tekkeon TekCharge with 4 AAs would be a better bet to get some charge into todays smart phones. Typical weight with 4 NiMhs will be around 280 grams (to give around 1 iPhone charge) compared to the New Trent iDual-Port Pack IMP50D 5000mAh External Battery Pack at around 155 gms (to give 2 charges). Using Lithium AA Primaries would give better performance (lighter weight) but would prove to be extremely expensive in long term use.

The OP is not entirely clear. Are we concerned about providing a full charge? Or are we just providing enough power to perform crucial tasks in a critical situation?

Sorry, I lost my thinking cap. If I run out of juice on an average, normal day, I have a fully charged backup cell phone battery that I can swap into the phone. The battery-powered recharger is for power outages that last more than a few days. I plan to keep a stash of, say, AA batteries so I can keep going in an emergency.

In your average power outage, I can afford to fully charge the cell phone, since I expect the power to be restore in good time, even if it takes the power company a while to do it. In a natural disaster, however, I may just charge the phone enough to do critical tasks. At the end, whether I get a full charge or not depends on how many batteries I have left. Portability is important in case I need to bug out.

This is what I'm thinking anyway. If there's something I've overlooked, please let me know. Thanks!

Da Bing

Thanks for the clarification. To follow up -- do you expect to have ready access to vehicles that operate on 12VDC? And, do you have a standard computer USB charging cable? If 'yes' on both counts, you may choose to add a 12V-to-USB plug to your kit, readily available for under $5.

Hey Jim, great first post. Welcome aboard.

"Learn to Hack, Hack to Live" is rather my motto. Out of inclination, rather than necessity. (Though beware the slings and arrows ...)

Hack away, sir, and kindly post your results.