i can't get my macbook battery to click in?

I took the battery out to look at the serial number because it was extremely slow and I was calling support. I'm not covered and don't feel like paying 50 dollars. Can someone please tell me how to get the batter back in? I know it seems like it should be a super easy process but it keeps getting stuck. Nothing is in the way and I've tried sliding in one side at a time and neither one is working. Any help would be appreciated!!!!