I just got this 15000mAh for $17 this game. It's pretty awesome so far, it's just pretty large. https://www.amazon.com/gp/product/B00JP8MZGK/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

As much as I'd like to recommend this, batteries that work with ANY USB device are a far better deal.

http://www.amazon.com/KMASHI-15000mAh-Ultra-High-External-Motorola/dp/B00JP8MZGK/ref=sr_1_2?ie=UTF8&qid=1439163209&sr=8-2&keywords=Kmashi+Battery

Get something like this. I bought one, and the 1 Amp port on it will charge your Vita. It's heftier than the official battery here, yes, but it'll also likely charge your Vita 6-8 times before it requires a recharge.

NOTE: Not every battery will work, the Vita seems to require a charging port that is "shorted" to work, so if you do buy a third party USB battery, make sure someone you know tested it with a Vita.