No it isn't. But we're talking about steam locomotives and all of the mainstream preserved steam locomotives that people go to see in the UK use coal as fuel. That's nothing to do with pedantry; it's just a fact.
The idea of disembowelling a coal fired steam locomotive and providing electric traction in its tender is ridiculous. I have seen preserved industrial steam powered equipment converted to run from a modern electric powered boiler. Crossness sewage pumping station in South East London is an example. But the difference there is that little is lost by this. The boiler room and its operations are not the main attraction. Instead that comes from the majesty of the Victorian ironwork in the equipment hall and the huge beam engines and flywheels which can be seen at close quarters. Here's what I mean:
The beam engines (well, the one of the four that's been fully restored) still work on steam and this can be readily made out.
Much of the attraction of a steam locomotive comes from its footplate; the firebox, the stoker shovelling coal and all the associated knobs, pipes, gauges and dials that go with the production of steam. Added to that is the general aura that the steam creates: the safety valve occasionally blowing off, occasional gentle leaks from the cylinders and carriage connections, the violent release of steam via the drain cocks when pulling away from cold, the exhaust steam blasting from the chimney when the loco is under way and working hard. These are what people want to see when they visit a heritage railway or go to see a preserved loco on the main line.
If all this is lost it would be best to keep the locomotive intact, "stuffed and mounted" in a museum somewhere. They could run a film alongside to show visitors what they've missed. They'll gain more from that than watching a once proud but now eviscerated locomotive being pushed along by a tender full of batteries.