Most of the time but not all of the time it's because the charging port it's self is malfunctioning or broken, or the phone has been plugged in and used too much .when it's plugged in to charge the wiggling of the cord and the temperature of the plug over heating the port cause it to lose connection and stop working. And like most people I've talked to like their phones but have no clue where to take them to have them fixed,well now that you can get the proper tool kits for phones from here and can buy the charger port off of ebay or Amazon for any where between $6-$30 you can save your self a big charge taking it to your provider and do the same Job yourself and in the process learn more about your phone and how to fix the issue again or on a friend's phone. YouTube has all the DIY videos on most to all phones,so fixing this issue is way less stressful.