A brief history: I use the 3GS as a bike computer of me our tours and their data records (B.iCycle). This brings about a problem that at the latest after about 2-3 hours of the iphone battery is dead and therefore no further function possible. After an intensive search and research have the Just Mobile Battery discovered. After a short inquiry by the seller, the Gum Pro as the 3GS introduced due out (Caution: obviously not fit all exteren batteries JustMobile to the 3GS!). In Gravis I later found a similar JustMobile battery with aluminum case and the same performance at significantly higher price. With a spare battery, the appearance and the case but I do not care more.
The battery is connected to the original Apple charging cable to the battery. Either during use of the Iphone or just in between to recharge. So far, it seems to me that the battery runtime by 3 to extend to 5 times. This means that our tours of 6-9 hours duration so no problem. The display 3 LED indicates the charge status.
The battery works reliably, is stable and compact. It makes a high impression, and it seems as if it may fall down sometimes without going broke. Information about the continuous use I can do until the end of this summer (2010).