How many spots are there in total? As long as there is capacity (spots) for any newcomer I would not have much of a concern about staying longer if you actually needed the charge. Two hours is quite short btw for signage. Four hours is more common. That lets you park in the AM and then move at lunch, or park at lunch and just drive home at the end of the day.
Those are Clipper Creek chargers and I do not believe they have any facilities for charging so I don't think that would be an issue.
Question: What voltage and amperage are the chargers? (I am trying to figure out how much actual money you cost them to park there) It is highly likely that there is no way you can actually cost them money since you are paying for the parking - I suspect the parking is more $$$ than the power they are providing. To the parking garage, what does it matter if you get two hours of charge and someone else gets two hours, or you get four hours and someone else gets none (I am just saying it is not a financial difference to them so I doubt they will police it).
I also feel it is extremely unlikely that they would tow you (a paying customer) for overstaying by an hour or two. If all spots were full and there was competition for the spaces that is a different story, but if lightly used I doubt anyone cares.
I do agree that having a note in the window with contact info is a nice thing to do. Here is one concept for that:
EV UFO / EVfrisbee - electric car Charging Notice - Frisbee - Electric Vehicle EVcharging EVcharger Tesla Model 3 BoltEV NissanLEAF evufo
I personally want one that says "I am opportunity charging - feel free to disconnect me if you require power or contact me at xxx-xxx-xxxx if you need me to move". I generally never *need* to charge for my around town trips, but I will charge if it is available.
We have four spots at my office parking garage and folks park there a lot without even bothering to plug in (that is a jerk move). The sign says limit 4 hours. After four hours the price on Chargepoint doubles which I think is a very fair way to keep people from parking there all day (but that assumes they actually plug in). The parking company seems like they could care less - often times these are only installed as they are required to in order to meet LEED compliance, etc...
My personal feeling is that if you are 100% sure someone is done charging and you have a way to move the power cord to another legal parking spot I have zero issues with folks unplugging and taking the charge cable to use. Chargers are a limited resource and once you are done charging I think they are pretty fair game. It is kind of nice that J1772 does not lock into the car by default so this is an option. I think the Tesla's are now unlocking when done charging to avoid freezing weather causing the solenoid to stick (but I have not verified this myself).
I actually don't have a problem with this behavior as long as they left some indicator saying "feel free to unplug me when done charging or after xxx time" and as long as that time listed was not over four hours. I actually think in many ways this is more polite (at least to other EV users) than parking in the EV spot. This way if another EV user shows up and there is no other stall with charge cord empty you can go ahead and park in the EV spot and if the Leaf is done you can plug in right then. If it is not done then you can park in the EV spot to reserve it and then you can come back and move the charge cord later when the Leaf is done (or when their 4 hrs is up). The only downside I see to this is if the parking lot is completely full and by leaving the EV spot open you are blocking a non EV user. One big plus side too is that say the Leaf only takes two hours to charge and you show up after that. You can then pull into the empty EV spot and immediately charge by moving the cable rather than having to wait up to another two hours for the person to move their car (in the 4 hr window).
