Before touchscreen and always on mobile Internet, our mobile phone can last for more than 3 days. Now frequent usage of facebook and twitter application, the phone can only last for half a day. Other bringing extra batteries and the infamous China made solar powered universal charger, gadget like Mophie Juice Pack Air Case for i Phone is cool to use. By the way I think we can’t bring extra batteries for iPhone.
Also they have universal power pack for all smart phone to juice up your travel day like this New Trent ifuel IMP500 5000mAh External Battery pack