Pumping more gasoline into your car than the tank can supposedly hold would be quite disconcerting. Yet with electric cars, the idea of supplying more energy than your battery’s capacity is an entirely normal scenario—one that you should get used to.
Last year, one of the leading car-charging companies, Car Charging Group, the owner of the Blink charging network, started charging by the kWh, rather than per charging session. And that’s definitely been cause for more owners to look at the ‘energy out’ numbers at the charging station.
In thirteen states of the Continental U.S., Blink is now charging between 39 and 49 cents to members and 49 to 59 cents a kWh to guests, for Level 2 charging. In California, Oregon, and Washington, Blink fast charging is also billed by the kWh.
Seeing the actual kWh numbers for your car may be a little bit confusing at first—because you might end up seeing that you’ve put significantly more energy into a battery pack than its listed capacity.
More kWh than called for
For example, when we were putting the Kia Soul EV through an extensive test drive a few months ago, one charge using a Blink Level 2 unit indicated we were paying for 27.83 kW—when the battery pack in the Soul EV is 27 kWh, and we still did have some (low) level of charge left.
Blink network - charging by the kWh
No, the commercial charger likely wasn’t off by much, if at all. Charging hardware itself usually has an accuracy within three percent, in terms of energy transferred at the charging port.
The real reason for the discrepancy is that you lose some energy to heat in the onboard charger. According to Kia, for instance, it’s typical for the onboard charger to lose 14 percent or more of the energy inputted on the way to the battery pack’s cells. Factor in charger inaccuracies (Kia notes that 3 to 5 percent isn’t unusual) and you could end up ‘officially’ putting in well over 15 percent more energy than the battery’s capacity, to restore it to 100 percent.
Not weights & measures, but certified
Energy meters used in charging systems are third-party certified, as well as govered by national standards and state regulation—as well as the requirements of the utility providers themselves.
Of course, there’s an official accuracy required of gasoline pumps, too. They’re under strict weights-and-measures oversight, with regular on-site inspections at the city or state level, and they’re allowed to be in error by about a half-cup, over a five-gallon test—that’s just over a half-percent.
Yet it’s not uncommon to see a gas pump that’s off by more than one percent, and at least one inspector reports of finding a pump off by about ten percent. And let's not forget that there are heat irregularities in gasoline, as it's dispensed, too, as it typically isn't adjusted at the pump for its lower energy content in hot weather.
Do you regularly charge with metered hardware, or pay by the kWh? We’d like to hear about your experiences with it, as a seasoned EV enthusiast or a newbie, in your comments below.