Solar panel output

Our MH was sitting in the driveway for about a month, we were not using and were away for a while, when I got home and went to to MH it was totally dead, lights would not even come on. I disconnected all the batteries immediately! I did not have it plugged in to shore power during this time. I knew that the house batteries were very weak, no surprise here, needed 2 new ones. The chassis battery voltage was reversed and read -9.5 volts, not a good thing, it was ruined! I was into finding out how this happened after disconnecting lots of stuff and finding a couple of blown fuses, I found that out of my solar panel controller it was putting out -19 volts, not a good thing! disconnected it and all it working well, haven't researched it any further yet. Just wondering if anyone else has ever had anything like this occur to their RV?