With it being a hire car, will they want it back with fully tank & battery?
Given that it takes about 6 hours to charge a PHEV at home and not everyone would have the means to do so, I’d say a firm ‘no’, they wouldn’t expect it to be returned charged. If they did (which I’m convinced they wouldn’t) then I’d just offer them a pound or two to cover the cost of them doing it 😂