Power bank or external battery case?


TS Rookie
My iphone 4S can not support whole day use as the battery nearly drain .

So I searched iphone 4S external battery in amazon and find Plush cartoon toys power banks AD below. The price is 29.99$ a little expensive as its 5200mAh. T

http://amazon.com/Constellations-Thunderbolt-Incredible-Blackberry-Fashionable/dp/B00DJ3DZK2 (avoild link, delet url space when past in IE)

Also I found a external battery case here :


The battery capacity is only 1700mAh but can be used as a case protector for iphone 4s

Which one I should bought or

do anyone find the similar high capacity like 10000mAh but cheaper one in ebay buy.com or amazon and other place?