As the title suggests. Had it just over a week. It will visibly hold on at 16% for example and then step down to 14% and miss out 15% altogether. On other occasions it has dropped from 31% to 29% in one go. Very annoying. My iphone 5 did this but with bigger chunks (18% to 14% for example). I've only charged it three times but never from totally flat. Any ideas?