It's a standard fitting on most plug-in electric cars: a visible light to show when it's recharging, often with a different indicator for when it's done.
Those lights, often on top of the dashboard and visible through the windshield, aren't yet standardized.
They come in red, orange, and green; some flash, some are solid.
And some other plug-in cars--the Tesla Model S and Ford Focus Electric among them--have a ring of colored lights around the charge port itself, rather than on the dash.
Now the low-volume 2014 Fiat 500e has a new wrinkle: an externally visible state-of-charge indicator that shows the battery's percent of charge.
It's similar to information that's available to owners on most plug-ins' touchscreen displays, often via a smartphone app for the car as well.
The low-volume Honda Fit EV also shows state of charge on a tiny display built into the car's remote control key fob.
Turns out, though, that not every electric car owner thinks the Fiat 500e approach is a good idea.
Tom Moloughney, who now drives a BMW ActiveE and previously had a Mini E, wrote:
I don't like the outside state-of-charge indicators, and don't want one on my car. I think a snappy smartphone app (I mean it works and it's instant!) would be all I need. I don't want others walking by knowing my SOC.
I can imagine it will lead to people unplugging you because they "really needed to charge badly and saw that you were almost full anyway."
I don't mind so much if the state of charge is shown somewhere inside the car, so you can quickly look inside and see it--but I definitely don't want something outside the car like what this pic shows. No way!
Honda Fit EV electric car remote-control key fob showing battery state of charge
"I think an external indicator that only shows if it is complete could be useful," suggested ActiveE driver Jon Jasperson, adding, "otherwise I do see a lot of charges getting interrupted."
Other owners, though, weighed in to disagree, saying that external lights were useful and appropriate in a large number of situations--and that they'd never experienced anyone unplugging their electric cars during a charge.
What do you think?
Should electric cars show their battery state of charge to the public at large?
Should they show only a light when the charging is complete?
Or is battery state of charge no one's business but the owner's?
Lave us your thoughts in the Comments below.