The problem is the batteries are a little old, and the voltage drop through all the switches etc before it gets to the Bdi, you can trick the bdi by charging momentarily so the charger pumps voltage in the batteries and raises the overall voltage but you disconnect before it's finished charging or drive it for 5 mins to lower voltage then charge it because it will say it's charged and stop charging, I am a crown tech, and we fit a relay at terminal board that bypasses batt voltage straight to bdi I think wire 2905 red white wire and a white wire on the board, -Ve on pump to coil, main relay voyage through relay to white wire on the board, this sends voltage straight to. Bdi