Range Rover Tdv8 4.4 limp home mode

I was towing up hill with my 2012 TDv8 4.4 diesel Westminster when it suddenly went into limp home mode. I managed to get into a layby and the engine died. I restarted it and it sounded like it was only running on a few cylinders and it would not rev. The battery then went flat and I could not start the car again. There were no error codes showing o the dash at the time. Anyone any ideas please?

If the battery was low, it might be a failed alternator and/or battery. Nothing works on these cars with low battery volts. Just a guess.