Acting weird/ not charging

So I have a Samsung Galaxy S III and when I tried to charge it today, it went red in the top left as normal but i checked it almost 30 minutes later and the battery icon was almost on the same state. The very bottom. When I turned it on it would turn on with 0%. and charging. Sometimes it would even be on 0 while not charging and stay on long enough for me to take a screenshot! What is going on with it?