Battery powered trains are a thing. Not all train tracks are electrified, even in Germany, and there are some places where a train line can be extended beyond an electrified segment. They charge through the normal overhead wire with about 1 MW with no extra provisions.

https://stadlerrail.com/en/flirt-akku/details/

These are new-ish to a point where only train nerds know about them, but they're also old enough to be a fully certified COTS product that you can just buy the way that you buy your normal trains also.

Considering how fast that industry moves, I think that is saying something.