I came up with a simple HW hack that works fine on my 30 KWH 2016 Leaf. Just mount a mechanical timer switch in series with the handshaking wire that goes from the J1772 plug to the EVSE. I used a 6 hour timer like this:
https://www.amazon.com/Intermatic-FF6H- ... mer+switch
With a 6 KW charger, I gain about 20% of charge per hour. So I just relabeled the switch face as follows:
The instructions I gave my non-technical spouse were: "Turn the dial to the remaining charge when you get home and plug it in. It'll stop at around 90%. If you want a full charge, turn it to 100%."
I tired it. It works. When the switch opens the EVSE cuts the power and the car stops charging. Importantly the car does NOT beep or complain and it still realizes the charger is plugged in, so you can't drive away and hurt something. If you add some time, the charge starts right up again. I figure the Leaf just assumes there was a power outage.
Note: You can install the switch at either end. I taped mine to the cable just behind the J1772 plug and ran tiny wires into the handle. The signal is low voltage and low current, so you can use any sort of small wire, like speaker or hookup wire. (Do not mess with the fat wires. Those are the ones that can kill you)
You might *think* "Hey, why mess with the handshaking signal? Just wire the switch to the latch sensor wire instead!" I tired that. It does work, but there is a problem. If you don't finish unplugging the car within 5 or 10 seconds of opening that switch the car starts beeping and flashing the blue LEDs on the dash. (It think the plug is not inserted all the way) I would NOT be popular with my neighbors if the car did that all night long, every night.
Finally, the charge rate I calculated is actually closer to 21% per hour. I rounded it off. Your charge rate will vary depending on the EVSE you have, which charger and battery option you have and even the age of the battery. My car charges at a very steady rate from 0 to 95% but then slows down a bit at the end.
I figure if I ever need a 100% charge and didn't set it up the night before, I just need to start topping it up about 45 minutes before I leave. According to the battery gurus it is still easier on the battery to top it up right before using it than to charge it all the way to 100% the night before.
Before anyone asks, I do NOT recommend using any sort of electronic timer switch for this task. If you want to use some fancy electronics to do the control, stick an old fashioned relay in place of the timer switch. You want the handshaking signal to just see a simple mechanical contact closure.