Electric car and in laws.

I don't have an electric car so I don't know but don't they recommend you don't use an extension cable? I believe they get very hot and worst case start a fire. Mines hybrid and has a slow charger so a plug socket is fine but not an extension.

I know loads of people do it but that doesn't make it "right".

When I looked into it, the £13 per night was similar to my figures BUT are they charging from zero miles? I'd imagine not.

Unplug it and tell them to go to a proper charging point and pay.

If they had a petrol or diesel car, they'd need to pay, so the same applies with their EV.

Cheeky fuckers.

I’ve driven an electric car for years and I think that’s cheeky of them. It’s essentially like getting you to pay for their petrol. Are they doing much distance each day. If they are only doing a few miles shouldn’t be much but the charge after the initial drive if they are a few hours a way will be more. You’d certainly be reasonable to ask them for some money but I imagine you are feeling awkward about it.

According to octopus home charging with a 3 pin socket can do about 10-13 miles charge per hour. At around 3pence per mile. The most itcwould be is around 20 pence per mile if charging at a fast charge paid point.
So assuming it's plugged in for 20hrs per night? Charging the whole time that's 130 miles, even if we said 10p permile that's £13 per night.

My guess is its not doing anything like that and is going to be a couple of pounds per night as the recharge the 20 miles they did that day.

If you have a smart meter can you check how much it is costing? They prob need to charge it everyday because it is less efficient using a.mains plug than a proper charger

A lot of holiday lets state that you can't use the mains to charge cars so it can't be cheap

I don't have an electric car, but I remember being pleasantly surprised at the cost on other similar threads so it may not be as bad as you fear.

I think it's about the bigger picture. Are they aware you're struggling? Have they been generous guests, for example treating you to dinner and bringing gifts? Or have you been run ragged doing everything and feeling the pinch financially from catering? Are they typically generous hosts to you? Have they been generous in other ways, such as paying for holidays, deposit, wedding etc?