The upfront cost is no longer prohibitive with all-electric buses realizing savings in the form of reduced maintenance and fuel costs that exceed the initial in

The upfront cost is no longer prohibitive with all-electric buses realizing savings in the form of reduced maintenance and fuel costs that exceed the initial investment discrepancy [1-2]. On your second point, a bus doesn't necessarily have to have a heavy steel frame for it to be safe. There are plenty of lighter weight (e.g. composite/carbon fiber) solutions which don't sacrifice safety. Sure, if the mileage requirements are low then there's definitely a cost-effective retrofit solution. But if you're a company already building a full electric bus and investing a lot of R&D into the pack design anyway, then you could probably just sell battery solutions to school bus companies as another revenue stream. I'd wager, though, that the larger addressable market is customers looking for new electric buses for longer routes. [1]http://www.columbia.edu/~ja3041/Electric%20Bus%20Analysis%20for%20NYC%20Transit%20by%20J%20Aber%20Columbia%20University%20-%20May%202016.pdf http://www.columbia.edu/~ja3041/Electric%20Bus%20Analysis%20... [2]https://www.nrel.gov/docs/fy16osti/65274.pdf https://www.nrel.gov/docs/fy16osti/65274.pdf