@Roberta Lynn, you're in luck! The US home office for A2B is in San Francisco

. You can reach them on the
weareA2B.com contact page or via email,
A2B.US@heroeco.com. Got to spend some time with Kyle Langdon of A2B at Interbike this year; he and several others of the staff are very familiar with the older Metros.
What makes you think that the battery BMS is shot? If this is the original battery the voltage might look ok, but it's not going to be outputting adequate amps, so it makes the bike either dead or the motor sounds 'grindy'. This would need a replacement battery which A2B has. If not the internal battery they will have the alternate rear rack battery.
Depending upon what is actually happening (you haven't given us any details) it could be a different issue relating to the motor & controller. There are 2 different versions of the controller/motor setup. Very early ones had the controller in the motor and latter models had a subsidiary unit near the cranks. Look for a serial number, probably on the underside of the bottom bracket which will help them identify which version you have.