The common technique is to drive in EV only from a full charge and keep going until the battery is depleted and the ICE kicks on. Stop and shut off the car and the trip summary on the dash should show how many kwh you've used. 5.5kwh or thereabouts is brand new. 4-5kwh seems to be about the common level of degradation for most. This is also the most reliable way to measure battery capacity and degradation. Kwh is not going to change (at least not significantly) with weather/driving habits/etc.. The 'guess-o-meter' with the estimated miles can be all over the place however based on all those factors.