The RS232 connection used to work well. Suddenly, when I powered on and connected RS232 to my laptop yesterday, I couldn't load the configuration from the controller. The controller indicated overheat fault flashing pattern. I also checked voltage of battery which is connected to the controller. I saw that the voltage value decreased from 13V to 8.5V after 3 mins. I use 12V battery.
Since you see that battery voltage 8.5 instead of V13, do the following. Disconnect everything from the controller apart from the power supply and check the current. If there is current then most probably he board is broken.