The battery had finally crapped out; it only started when plugged in. Microsoft Store confirms this. Now, note.... the Store is there to SELL things and I get that the guy I talked to was a SALESMAN. However.... empirical evidence also led to this diagnosis.
SO. The cost to replace the battery in a Surface is $450. Backing up the Surface to the cloud is $50 and takes a day. A NEW base model Pro6 is $700 (all this is without tax).
