What do you call the battery slot's ends? By that, I mean the spring and the little round flat end for the plus and minus ends of the battery. Do they have a name? I looked up on the Internet, but couldn't find anything.
They are called contacts., or alternatively, terminals.
A battery holder is a cavity or compartment used to house one or more batteries in a piece of equipment safely. The battery holder has flat metal or spring coiled contacts that press against the battery terminals making an electrical contact.