Same thing happened to my iPad 2 a while back. For me, it charges when it is powered off, meaning when it boots up, turn it off immediately and it should charge fully. But, you will find, The port does not work for syncing either, so make sure not to disable your iPad! I learned that lesson the hard way. (Now I can’t reset it using iTunes so it’s basically bricked.) Anyways, I think It’s the Power Jack that’s the issue. (If you’re lucky, it’s not the logic board, which is like the motherboard for mobile devices). Just take it to an Apple Store and have them repair the Power Jack, and Boom, you’re done!