Proterra claims 70% reduction in maintenance costs and this seems reasonable. There is a lot of engine and transmission work in a diesel bus that makes up a lot of the scheduled maintenance. You can’t maintain something that does not exist! As with most EVs, brakes last 2-4 times longer as most of the braking is done with regeneration by the motor and battery. Over the long term, batteries may need to be replaced as their capacity declines. This is similar to engines and transmissions that are often replaced in diesel buses. Diesel buses often require rebuilds to extend their operational life that may amount to 50% or more of the replacement cost of the bus.