The big black thing clipped to the metal battery strap is a 30 amp fuse.It pulls apart and there's a blade type fuse like on a car but it's really big compared to a car one. It's a good way for disconnecting the battery if you need to work on the electrics without taking the battery off.
You probably tightened the negative battery terminal the first time you put the battery on, the problem with the earth strap is you want it to point up and dowm. if it's pointing in toward the center of the bike when you push the battery back into place it gets pushed into the vertical and twists under the battery bolt slackening it back off.
