I had a dead battery too, I charged the 3 module with an adjustable Transformer, bridge rectifier and some incandescent Light bulbs from 25 to 300 Watt, as inline resistors. My Battery showed also no Communication with the three modules. While charging the battery manual and i made sure the individual cell stayed below 4 Volt and they stayed balanced. I got the 3 bank to 113 Volt and reinstalled the battery. Now I could read the voltage of each cell through the can bus with my OBD2 reader. But P18051C was now also present and various other HV circuit fault. The BMS is on it way to be reset. The Battery is open in my garage. It over a month since I charged the battery and it still show 111Volt per bank.