Does anyone have experience with external batteries? I usually just buy extra batteries for things like five hour plane rides, etc., but I've got the verizon case with the kickstand (which I'm loving) and I'm not sure I want to keep taking it off and replacing it every time I need to replace the battery. It seems like the case fit would just get loose after multiple removals. I saw some external batteries during my research and figured it wouldn't be to bad to have the phone and an external battery sitting on my tray!