I carry an iPhone 3, which means in a couple of hours of tweeting, my battery indicator shows red. The Apple store chargers or battery backups for iPhone were an expensive options, here I bought this as a cheap solution for my iPhone battery woes. Check out this video review below of this 4 way phone battery charger from Chroma available at Chroma Stores.
Trial day 1: I used the 9V battery (chinese made) for charging, it surely charged my Iphone to about 90% , but then the battery was useless. So cost of a single charge Rs 80/- . Verdict: Too expensive.