I think many iPhone users have the experience of running out of battery. But you may not know there are external battery for iPhone in the world. I would like to introduce you the MiPow Power Tube 3000 (3000mAh).
Unlike some knockoff products or universal products claim to be worked for iPhone, our products are "Made for iPhone" certified which means you can use it to charge your iPhone without worrying it would break your devices.
It is very user friendly as it has built-in Apple 30-pin connector to charge your iPhone directly and thus you do not need to bring extra cable with you.
http://www.mipow.com/product_detail.php?pid=32&lang=en
Unlike some knockoff products or universal products claim to be worked for iPhone, our products are "Made for iPhone" certified which means you can use it to charge your iPhone without worrying it would break your devices.
It is very user friendly as it has built-in Apple 30-pin connector to charge your iPhone directly and thus you do not need to bring extra cable with you.

http://www.mipow.com/product_detail.php?pid=32&lang=en