Not sure about this, if you are looking for a slim Power bank, Anker makes a Slim 10000mAh for less than $30 here: http://amzn.to/2FhV1bp
However, I see that it is a wireless power bank which is kind of cool. But you would have to keep your phone on it to charge. Maybe see if they have some kind of warranty just in case it stops working. That is whats good with Anker products, it is backed by warranty.