An Atypical Day

Mercedes B Class EV

Earlier this week, I needed to drive my wife to the airport (about 30 miles from home), after dropping the kids at school, then find a spot to do a conference call and finally get home before the traffic gets too bad heading east over the San Francisco Bay Bridge so I can pick the kids up from school. All told, the round trip was 65 miles. Easily in range for our Mercedes B Class on a single charge so I plugged it into our eMotorwerks JuiceBoxPro the night before and we set out in the morning on a full charge.

Indicated Range

The indicated range dropped pretty rapidly as we set out because the ambient temperature was around 50ºF (10ºC) which requires the battery to be heated and drops the mpkWh from the normal 2.5 value to around 1.5. After we got going though, the consumption number steadily climbed back up and the estimated range stayed pretty much constant.

After the drop off I headed to Colma, just south of San Francisco and along one of my routes home from the airport, because of this:

Chargepoint Map (Colma, CA)

Unlike most of the charging locations in Alameda, those 4 Chargepoint chargers at Kohl’s in Colma are usually available. When I arrived, three were available. So, I plugged in and then walked a short way up the hill to a nearby coffee place to do my conference call and get some work done while the car recharged.

Three hours later, I was back at the car and heading home on a full battery again (having added 15 kWh according to the Chargepoint stats).

At the end of the day, the car reported this for the overall driving stats:

Trip Summary

As you can see, the average speed is not great (the drive home was stop-start traffic for about 1/3 of the distance, as was part of the drive to the airport in the morning, and around our home town of Alameda the speed limit is 25 and there are stops every block, so we normally average around 12 mph there). The battery ended the day at just under 80% too, thanks to that charge at Colma.

Also worth pointing out that the 2.9 mpkWh number there is adjusted by the car to account for the losses in the charger (the best estimates I’ve seen for this are that the actual mpkWh is 20% higher, although to be fair, the discounted value is a better estimate of the cost).


To do that journey in our ICE SUV would have used about 3 gallons of gas, at a cost of around $10 currently here in California. In the EV, thanks in part to the free charger at Colma, the round trip essentially cost us about the same as a gallon of gas, or one third of the amount we’d have paid using the ICE car. That might even go down more if we happen to get a free charge later this weekend in Alameda. Without the free charge, the cost of the journey would still only be about $5.

We also gained a small saving from the being allowed to use California’s car pool lane over the Bay Bridge – one of the state’s incentives for driving an EV is access to car pool lanes with less than the required number of drivers.

Aside from the monetary savings, using the EV also reduced the carbon footprint of this journey dramatically.

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