My 2014 GM L1 EVSE (Clipper Creek OEM) uses 2W at idle. The 2017's could be lower, but I haven't heard of any actual measurements. If you pay $0.11 per KWHr, that's $1 per watt per year (good rule of thumb), or $2 per year for the EVSE plugged in 24/7. Remember that standard outlets are not designed to be plugged into every day, they will loosen up over time, requiring replacement.