I'm pretty sure the cable is dying because I haven't had the problem till recently, I know it's not the charging port on my iPad because it looks pristine and I have only had it since last July, I was also using the charging brick it came with and the cable is not from Apple but when I use that cable it charges just fine and I don't have the not charging issue
Read more: Why does my lightning cable charge my iPod touch and not my iPad?