Here is a kilowatt-hour energy meter I just finished putting together. It keeps track of the total KWH used, showing it on the digital display in 0.1 KWH increments - and with its L6-20 connectors it plugs right in to the modified EVSE. The meter works on 120 or 240 volts, just like the upgraded EVSE. There is also a small "impulse" light which flashes 800 times per KWH. At 240V that's almost one flash every second. At 120V it's about once every 3 seconds. So, you can get an idea of the current energy draw based on how fast it blinks. The meter is not resettable, and the memory is retained when unplugged.
The meter is small and easy to carry along. If you leave one at home and bring the other one in the car, you can know how much of your own electricity you use when recharging at home and also how much energy you use when charging away from home. If you need to borrow someone's outlet, you can plug in the meter while charging there and they will know exactly how much energy was used. The project is not quite finished yet - I need to do a little more testing and put it in a nice weatherproof box, and the cord connections will be much nicer - but hey, it works!
Here are some photos while testing:
Closeup photo. Display shows 0.6 KWH so far:
Here we are plugged in to 120 volts - and we're up to 1.8 KWH now:
Here we are plugged in to 240 volts: