It's been mentioned before, but school busses are the ideal implementation of pure BEV. Their operation time to charge time allows them to be far more gentle on the batteries than mass transit, where you might only have a 4 to 6-hour non-revenue window to charge a whole fleet of busses that need to run for 18 hours at a time.
While the upfront and maintenance costs can be considerable, for mass transit, spending at least part of the route running and changing on trolley wire is a much more sustainable option.