Check the center post on the battery it may have gotten forced down .
I'd agree with this. You can really carefully pry up the center post on the battery. Make sure it's turned off and gently, ever so gently pry up a tiny bit on one side, then move it a little and pry up again. Repeat all around the center post.
You can use a small screwdriver if you have one, but I can't stress you need to move it the smallest amounts otherwise there is a good chance you will break the wires and render the battery useless.
Just remember, when screwing toppers on to your battery it just needs to make contact, not be super tight.