These things are hybrids : https://en.wikipedia.org/wiki/New_Routemaster
https://www.londonreconnections.com/2014/future-london-bus-part-1-new-routemaster/
Surely the dirty old ICE bit can scooped out and replaced with a big battery? Also, maybe wireless charging : https://bus-news.com/london-new-fast-wireless-bus-charging-introduced/