@Karen3224 There's no set policy on whether to charge for an optional amenity, but to collect payments via AIrbnb you have to send the guest a resolution request, and the guest chooses whether to accept the charge.
For this reason, charging based on kwH consumption at the end of the stay is not ideal. You don't want the freshest thing on guests' mind when writing their review to be getting asked for money. One alternative would be to advertise a flat daily fee to make the charging point available.
On the other hand, the promotional advantages of offering a sought-after, searchable amenity as an inclusive feature should offset the relatively low cost of use. Unlike other popular amenities such as swimming pools and hot tubs, the EV charger doesn't add greatly to your home expenses, maintenance costs, or cleaning time, but it can still attract some guests who might not have otherwise traveled to your location. Personally, I'd offer it without fees for a trial period of a few months and see how it impacts business. If the cost becomes problematic (perhaps due to volatile wartime energy costs) it will still be possible to make it a paid amenity later.