Have the Gum Pro 4400 now getestet.Er three weeks has a total of 218% charged my iPhone 3GS, ie twice from 20% -98%, and even more by 18% -80%, then the battery was empty. The charging time was respectively as fast as loaded with power supply (about 2 hours) .I think that is probably sufficient as Ersatzakku.Da I other plug batteries as zBden solar battery and the battery with the three blue LEDs (there's at eBay in white or black), have just had a bad experience, I can recommend this here fully for the 3GS, the other can your expensive 3GS "scrap" .Glaubt me das.Ich and my friend, we have experienced it firsthand. And to prevent more people destroy your expensive 3GS, I've written this recession .So the Just Mobile Gum Pro is the ideal companion for 3GS users .He works naturally with all appliances that can be charged via USB, z. B. also Ipod Nano, PSP, PS3 controller, Nintendo DS, iPod touch, etc. I hope my report has helped you a little ;-)))))