Power Banks for charging electronic devices come in many shapes and sizes. I recently was made aware of a real tiny one which I believe is the smallest one I have ever seen from USB Depot called REUM High-Speed USB Charge Adapter this one comes in an orange rubber case that has a clasp that could fit on any key ring, backpack zipper or anywhere you want to attach it. This is a fast speed for your PC, automobile USB port, AC charger for home usage, Smartphone, tablets and more. REUM charges Galaxy S3 in 2:56, Galaxy Note 2 in 3:10, iPhone 4S/5 in 2:10 and lastly iPad2 in 3:50 those seem like pretty fast charging times. The way you use it is on the side there are the letters A stands for Apple products and white LED light, D stands for Sending data 480Mbps data communication with the computer and LED extinguisher and S stand for Android Phones and a blue lED light.
My Opinion: So I attached the USB cord to my computer and then to the phone which went very snug into I have an Android phone so the blue light came on when I looked at the phone it had the sign for charging so that is a plus. I think this would be great for traveling as you can charge your phone right through your laptop instead of carrying so many different cords and plugs.
To see more visit https://www.customusbdepot.com/product/turbo_charger#.V0IIQZFJnT9
Disclaimer: I was in no way compensated for this review and this is solely my own opinion which may differ from yours.