We have a V2G charger/discharger connected to our leaf, on trial with Ovo. It's 7kW max, but generally charges at 5kW, discharges at 3kW. I think it has pretty high idle, taking somewhere around (or possibly higher than) 1-2kWh/day continuously - it's very hard to measure accurately though. When unplugged it's a lot lower, that number is for when plugged in (contactors engaged in V2G box and in car, and there's a fan on in the unit & it's all ready to go at a moments notice). It's hard to measure, as the cables are hard wired in place, and it randomly (to me) charges or discharges every now and then. Before that we just used the granny cable - the main objection I had to that was that it charged to 100%, and it isn't great for battery health to keep doing that. In fact, the leaf battery warranty specifically mentions continuously left charging at 100% as a problem. If we weren't on the trial, I'd probably have got a Zappi, which is an intelligent "Evse", telling the built in car charger how much AC current to draw. I think you can control it from your 'phone, and tell it to use "spare" solar, etc.