We carry the B&D VEC1093DBD 40AMP Portable Smart Mode battery charger as a back up plan.
Have you looked into why your current on-board converter/charger is not working. This may be as simple as replacing a couple of fuses or resetting a DC Circuit breaker to return your converter/charger back on-line.
The converter/chargers are pretty resilient but do have protection devices like FUSES and CIRCUIT BREAKERS to trip when problems occur with the battery system.
What have you done to determine the converter/charger defective.
Roy Ken