Andrew,
I know of one other owner who had the same problem with their bow thruster motor. They had Amel in Martinique ship the motor to Amel La Rochelle, who shipped it to some unknown place for rebuild. The total cost was between 3,000 and 4,000 Euros!
When you have a chance please share your information, because even though it is located in Perpignan, France, it may be a solution for boats located elsewhere.
It is interesting that he suggested a possible cause might be the bow thruster solenoid switch. I had not considered that too much resistance in the solenoid would cause damage to the motor and communicator, but I now understand how it could. I
do not know the specs of the thruster relay on a SM. I can't get to mine right now and will look later. I suspect that I will find some numbers on it that I will search.
Regarding your batteries, they can be checked for internal shorts and load-checked. I am sure that you know that most battery suppliers will provide this service.
Thanks,
Bill BeBe 387
Trinidad