Carwings shows efficiency that is different and higher than what Leaf shows. I've been tracking this for a number of days now. Every day I note down Leaf's efficiency i.e. miles/kwh figure and reset it.
As you can see the carwings can be higher anywhere from 10% to 35%.
This is the response Nissan sent to Andy on this problem ...
Discrepancy between carwings energy economy, and the miles/kWh indicated in the car
I apologize for the inconvenience. The shown average energy economy is different on the vehicle and website because the vehicle calculates with power-loss in motor. However, the website excludes power-loss in motor. This is actually a known issue that we are working to correct. Unfortunately, it will take some time for this to be accomplished. If you have any additional questions, please do not hesitate to contact us.