One of the reasons I got the VW Droid MAXX last year was it had a battery twice the size of most phones at the time. But there were times when I still needed a quick charge when I don't have access to wall outlets. I had several portable batteries that worked with my prior Droid 4. But they don't work with the Droid MAXX at all. When connected, some show the phone is charging for a few seconds, then it changes to not charging. Others never even show the phone charging when connected. Any thoughts/ideas why?