You are dealing with clandestine BAD CONNECTIONS where the panel connects to the system. Like a rotten oak, everything looks peachy dandy from the outside until the tree falls on you. Dig into ALL of the connections at that site and get them in first class condition. Has the controller magically turned into a heater? Connect and put your hand on it 5 minutes after reconnection? Does it feel like a griddle ready for pancake batter? Do this test after you dig through and repair all those connections. Do the battery too.