I received the dreaded e914 @ about 300 miles, cycled the power and continued up the trail then my bike completely shutdown. Took it to the local dealer and found out I was the 3rd Moterra SL owner to have this error. One bike only needed the connector cleaned, one received a new battery, and my bike received a new battery and drive unit per Shimano.
I only have about 15 miles on the new equipment, and other than a slight loss of efficiency riding @ 4* C, the new battery seems fine..
The downtime was a little longer than I would have liked waiting for parts to arrive, but these are machines with electronics and will be prone to failures.