What size is the alternator? What size is the wire to the battery in wire gauge size (14ga to 8ga)? A wire will heat up if the wire size is too small to safely carry the amperage load. Here’s a handy guide:http://www.powerstream.com/Wire_Size.htm
If the gauge size is appropriate, then something is causing a major drain. A short in the battery can do this. I’ve personally seen a battery with enough juice to start a car, but still pull enough current from an alternator to fry it in a heartbeat.