Iphone 5 Battery Charging Acting Strange

The last few days my Iphone 5 has been acting strange with charging the battery. I will be charging it and it will not go past a certain number then if i unplug it a couple times or restart it then it says 100%. It will be ok for a little while and then go through the same thing. Yesterday my phone said 36% and a couple minutes later shut itself down because it was a 0%. So the number is just not reading correctly.

Is this just as simple as changing the batter most likely? Or something else, other than this the phone works fine as far as i can tell