This Battery Safety Monitor (BSM) board is a PCB that reside in the Roadster ESS battery pack.

It controls vital functions in the pack, and communicates through CAN signals reporting battery conditions.  The assembly is buried inside the battery packs and requires a battery pull for service.

There are some electrolytic capacitors and a relay on this board.  , this assembly needs a rebuild every 8-10 years since that is the service life of large capacitors. 

Fortunately, this part is repairable and rebuildable.  We have successfully reverse engineered this sub-assembly, have schematics, and are offering full rebuild services.

Around 2000+ Roadsters are running around with parts like this aged 10+ years.  We recommend rebuild of the electronics buried in the ESS Battery Pack, including the DC-DC Converter, whenever a battery upgrade and battery sheet replacement is done.