My 1998 XJR had been turning over slowly and eventually refusing to crank on occasion. Before I had a chance to look at the problem, I had an electrical smell coming from under the hood, so it became Saturday morning's project. The battery cable to starter cable connection that passes through the tool tray plastic bulkhead stud was loose, causing the problem and not allowing the battery to fully charge, since it's also the charge route from the alternator. An hour to clean and reinforce the connection fixed all my apparent electrical problems. It's good to check on occasion. Make sure you remove the negative battery cable before messing with it.

 

Yes, electrical resistance is a common cause of heat and smell. Another common fault is the ear the strap underneath from the bell housing to the chassis on the LHS. Worth to check that too.

 

Hopefully you cleaned the threads of both the stud and nuts as the electrical path at some points must traverse the threads.

The design of that connection is horrible.