A lot of science goes into electric cars, but when it comes to gauging battery-charge percentage, there may be a little more art involved.

In this case, the DC quick-charge stations that are currently being installed near highways along the U.S. West Coast – and other locations – can't communicate with precision with electric vehicles to calculate the correct state of charge (SOC) percentages and will likely overstate the true amount of charge in the EV, according to one electric-vehicle advocate. And that could cause drivers to miscalculate their cars' available range and, well, come up short.

Tom Saxton, vice president of Plug In America, wrote on his blog about his experience quick-charging his Nissan Leaf at an AeroVironment DC Quick Charge station in Washington State. Saxton said that, charging at stations like the one he used don't know exactly how much energy is in the car's pack and so can display an almost 100-percent charge, but the true amount of energy in the pack can be closer to 80 percent. For a car like the Leaf with an EPA-rated 73-mile single-charge range, that could leave a driver about 15 miles short of his or her intended location.

Part of the issue is that when using a fast charger, a Leaf will only "fill up" to an 80 percent charge after starting from less than a 50-percent charge. This means that what appears "full" on the station doesn't mean "full" in the car, and there's no way to get the station to figure out what the actual situation is.

The solution? "Ignore what the station shows" and use the EV's on-board indicator to properly gauge the charge, Saxton writes.

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