@Tasha459 Of course electric rates vary in different areas, but about $6/day for a full charge seems to be what I've read is the approximate cost. If the guests are only there for a few days, I'd let it go, but if they are longer term, you might want to discuss it with them. And put something in your listing info about where the nearest charging station is if you don't want them charging at your place.
But this is going to become more and more common, so hosts should probably come up with a plan on how they want to handle it.
Here's a fairly recent thread where this topic was being discussed:
https://community.withairbnb.com/t5/Host-Circle/Can-I-plug-in-my-electric-car/m-p/1535188