Has anybody got any suggestions on this one?

CDIIMax runs fine on diesel, charging O.K.

Runs fine on electric most of the time then other times the customer comes in to find the fridge has stopped and the battery is totally discharged.

The alternator brushpack is new, several other trucks run off the same mains power circuit and they are all O.K.

There is no sign of a drain on the battery i.e when you attach the jump leads there is not even the slightest spark.

We've had it at the workshop for 3 days and it ran absolutely perfect.

I've checked all the usual CD problem areas where the wires chafe but they are alright.

Ideas anyone?

Regards,
djbe.