http://www.walmart.com/Music-Power-Encore-Rechargeable-Battery/ip/5750793 Well first of all you can beat the price of $12.98. It obviously has dual usb so you can charge two devices at same time. Well I tried it last nite for the first time, I let my droid get to 20% battery life then I plugged a fully charged extended battery I got from walmart and then I waited to see how much it'll charge my droid before the extended battery died. Well, it only charged it from 20% to 60%. Again, not bad for $12.98. Also 40% extra charge on a droid is good for a couple hours until you can get to a wall outlet or what have you. good enough for long road trips or plane flights. I recommend if your strapped for money cause they obviously have pricier ones out there. Link above if you wanna get one..