I've been using Belkin 4000mAh for quite sometime. Can charge up to 3 or 4 times depending how much % left in my 4s / 4. Love the fact there's 2 USB output ports, can charge 2 phones at once.

Got it for around $40, now it's $23 AUD.

http://www.thegoodguys.com.au/buyonline/Be...000mAh_F8M160AU