Silverstone Teratrend PB05B Pen Shape Mobile Charge AA Battery X2 Aluminum Black

Comment:
This is the kind of backup power pack I always wanted. Battery will die after 1.5 year. But USB regulator will last a lot longer than that. With a replaceable battery pack, it makes all the sense !The price is right. Compare to some over $40 battery pack, it is definitely a good solution. 2 AA batteries you can find it anywhere. A rechargeable battery is a good fit too.However, may be it is too compact. 2 AA batteries does not have much power. I can only charge my S3 up by 20%. Way below my expectation. Of course, mathematically, I can charge my phone to 100% by 10 AA. But that is not the point.Overall, I still believe it is a solution on the right track. It is just I expect too much from 2 AA batteries.

Comment:
So I got one of these as soon as I got my HTC One. I threw some Eneloops in it and it definitely charges the device. I find I get about 25% charge out of it. Which is alright, but the output is slow enough that while watching a movie in 720p, the battery still went down 3%. So basically these are a good backup as a just in case, but if you plan on using them often I would just get a dedicated portable battery bank which are usually about 3000mah and 40 bucks.