I download the data straight from SDG&E's meter, and find the Blink to be understating the consumed power (during charge) by about 1.5%
ECOtality removed the one "dashboard" tile that was most useful from their web site dashboard -- it had the Blink-reported power out to the milliwatt (literally). Since then, I've stopped using the Blink reporting and just ask the meter how much power was consumed. After all, this is what my bill will reflect.
I've run the car down to turtle, then parked it with the heater on, then left it on with the fans running for hours. The lowest SOC reading I could get was "3".