Anyone has some advise about power bank?

[Guest rackas]

A newbie here, My 9100 battery now nearly drain can not support whole day using.

I want to get a spare battery and find something like power bank very popular in amazon AD like :

amazon.com /Constellations-Thunderbolt-Incredible-Blackberry-Fashionable/ dp/B00DJ3DZK2 (avoild link, delet url space when paste in IE) 5200mAh

Also Anker spare battery : amazon.com /Batteries-GT-I9300-T-Mobile-U-S-Cellular-EB-L1G6LLU /dp/ B008AGA6PK/ only 2000mAh

But it is not the original samsung replacement. And I also found many "Samsung" battery but the merchant is not the samsung company.

Which one I should bought? Do anyone use them can give me some advise ?