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I wanted to use this device (Portable USB Emergency AA Battery Powered Charger) for charging various USB devices, including cell phone, MP3 player and tablets. Its output is rated for 5V 500mA, similar to that of a standard USB 2.0 port. So anything you can recharge from your computer's USB port, you can recharge with this device. But obviously you cannot use it to recharge an iPad, because the latter requires 2A of current.

The device is powered by two AA batteries, either rechargeable or disposable. The down-side of using AA batteries is that it has much lower energy density compared to rechargeable lithium-ion battery pack. The up-side is that you can quickly swap in another set of spare batteries. The fact that it accepts alkaline batteries could become handy during an extended power outage.

I tested this device with two eneloop AA NiMH cells inside. I connected a 10-ohm power resistor as load, and recorded the output voltage and current using the PortaPow USB Power Monitor. The device was able to generate an output of around 4.7V at 0.47A, for 78 minutes. This corresponds to just 2.9 Watt-hour of total output energy (4.7V * 0.47A * (78/60)h = 2.9Wh)

To put this output energy in perspective: my Samsung Galaxy S3 has an internal lithium ion rechargeable battery rated '3.7V 2100mAh'. This corresponds to a total energy of 7.77Wh. Factoring in conversion losses, I'll need to empty three pairs of eneloop AA cells just to give my S3 one full charge. This is hardly practical.

Some Other Notes:
- With the switch in OFF position, the output is not completely cut off. It still shows the internal battery voltage of ~2.5V.
- The sliding battery door is difficult to open if you grab on to the middle of the case. But if you pull from the bottom of the case, it slides off easily.
- The LED light on this device is quite useless. It draws just 0.4mA when powered by two NiMH cells (2.6V). The current increases to 2.7mA when powered by two fresh alkaline cells (3.2V). So the LED's real purpose is to serve as a battery tester.

[Bottom Line]
Given its low cost, this USB charger is still worth considering if you only need to recharge low-power devices such as MP3 player. To recharge anything more demanding, you should get a power bank unit with Li-ion rechargeable batteries inside. For example: the KMAX-812 4400mAh Rechargeable Backup Battery Pack is just slightly larger than this device, but it can deliver about 5 times the output energy (15Wh vs. 3Wh). Plus it packs a real powerful flashlight.
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on February 11, 2014
I am still searching for the perfect solution. This is not perfect but the best I have found so far. They will convert AA batteries into an iPhone charge. I use my Iphone5 as a GPS, camera, notes, iBook, music etc while camping and as an email machine while traveling. I need a lightweight charger that runs on 2 (not 4) AA batteries. This thing works great. What I don't like is that the batteries get hot, which is not a problem winter camping (hand warmer) but a valid concern on a plane. I have never had smoke but they do get hot. I tried the modification of clipping one of the middle pins on one but it wouldn't charge after that; I may sacrifice/test another one. I have also bought one or two defective ones so I buy/carry extras. They are cheap, lightweight, compact and disposable. I would pay more money for one that doesn't get hot but I can't find a 2AA with decent reviews. These things work well for charging an iPhone. The flashlight is better than nothing but not by much. They are not perfect but certainly worth the price.
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on February 28, 2014
I have had this charger for over a year and have used it several times. It is great to have on the go and in an emergency, just have some AA batteries on hand and a USB charging cord for your device, & you are good to go. I have charged an I phone; MP3 player, and an LG cell phone with it so far. For the price, it is a very good deal. A good addition to an emergency kit. It does get pretty warm when it has been charging for a while, not sure how hazardous that is, as I have seen batteries get hot in cameras, RC cars, and other devices before,(during heavy use). I would be careful and not use the charger on or around any flammable materials just to be safe. Maybe alternate batteries when they get too warm.
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on September 14, 2014
This thing is great, the light does not do a great job as a flashlight but is nice to have in a pinch, great for finding keyholes and such when you don't need a real flashlight. It's mainly great to have as a battery charge indicator. The batteries do continue to drain while it is switched to off so I recommend not storing the batteries inside it, especially since the switch is sensitive and can easily turn on in your pocket. But the usefulness of being able to charge your devices from AA batteries is super handy. I'm going to be ordering a couple more of these to keep next to our batteries in our household and camping supplies in addition to the one i carry with me.

I've used it on a couple occasions to test "dead" batteries to see if there was a response from the light, those batteries then can go into remote controls and get quite a lot more use before being actually dead.
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on April 15, 2014
The "emergency charger" actually does what it says. The unit has a built in white LED light activated by a switch on the side. The switch allows the user to select between "light, off, and USB." It's slightly larger than the two AA batteries it contains. The battery compartment is accessed by holding the top (by USB port) with a thumb & forefinger of one hand and gripping the bottom of the unit with the other hand and pulling down. There is a diagram inside that illustrates how to insert the batteries. I tried it on the iPhone 4S and it seems to charge the phone without issues. When the switch is in USB mode there is a red LED indicator light that activates on the top side of the charger. Other then the slower then usual shipping no problems.
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on June 10, 2014
I've bought a few of these type things and most of the time they don't work at all.

These work pretty well, at least for maintaining battery and moderate recharging.

So, considering the flexibility of using AA if you, like me, already have recharcheable batteries as the foundation of your electronics system make them a really good choice.

The additional LED light is nice to have, but I fear the ergonomics of the switch will create inadvertent battery depletion if the light gets clicked on. Also, in a hurry, and everyone who is really in a hurry will understand, if you push the switch the wrong way it may not charge your device. I prefer no-brainer ergonomics in these type devices.

Also, the battery cover is kind of annoying. I wish there was a version that retained the batteries well enough that the cover was not needed or at least was easily used or not for aesthetic reasons only.
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on September 15, 2015
with good batteries to put in this, you get a range of hours of dependable charge for your cell phone. I am amazed at the power it supplies with good batteries - batteries not included, for your info - so the strength of your addition depends upon the batteries YOU supply. This is a great back up.
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on September 19, 2015
This was intended to be a backup for my iphone 5C while backpacking. It works. I kept the one of the batteries in backwards until I needed it. It charged the phone a little bit, enough to get some messages and calls out at the end of the hike. It's light weight and size made it ideal for this application. Now I keep it in my daily carry bag, just in case, but I have only needed it once and was glad I had it.
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on December 6, 2014
Really only helpful in a desperate situation. Provides minimum charge. One shot deal, then you have to replace the batteries. Benefit over rechargeable charger is that you don't have to repeatedly charge it between uses.
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on December 17, 2014
Love it. I'm using it with my GoPro cameras. Seems to work very well! The cameras charging light blinks the whole time. Looks like I'm not even using the internal GoPro battery. I bought 3 of them!
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