It's one of the most frequently asked questions by anyone hearing about a modern electric car: do I have to replace the battery?
With 15 years of experience in mobile phones and more than that with laptop computers, most buyers know that lithium-ion batteries lose capacity over time.
Replacing phone or laptop batteries, generally for less than $100, is irritating but not a deal-breaker.
The specter of replacing an electric-car battery pack costing several thousand dollars, however, may well be.
The question arose most recently when Chevrolet included the following wording in the owners manual for its Bolt EV 238-mile electric car:
Depending on use, the battery may degrade as little as 10 percent to as much as 40 percent of capacity over the warranty period.
2016 Nissan Leaf
There are two things every buyer should know.
First, yes, electric-car batteries do lose capacity over time—though not nearly as fast as those for consumer-electronics devices with a 1- to 4-year expected life.
Losing 10 percent of capacity over an eight- or 10-year warranty isn't too big a deal, but losing 40 percent would be—though that's likely to be only in very, very limited circumstances.
ALSO SEE: Nissan Leaf Battery Capacity Loss: Covered By Warranty, Now (Dec 2012)
Second, electric-car makers warrant their batteries against excess capacity loss, though the warranties vary considerably.
And this is where reader Gary Exner of the Oregon Electric Vehicle Association comes in.
Battery warranties for 12 battery-electric cars sold in the U.S., Dec 2016 [created by Gary Exner]
He sent us this useful chart of battery-capacity warranty terms for 12 different battery-electric vehicles now sold in at least parts of the U.S.
(The information will be easier to read on most devices if you click on the graphic to embiggen it.)
He pulled the information, he said, from online manuals and warranty booklets for the different cars, with some filling-in from the carmakers' websites as well.
You'll note that some electric-car brands (BMW, Chevrolet, Kia, Mercedes-Benz, Smart, and Volkswagen) warrant battery capacity at various levels.
Others (Fiat, Ford, Mitsubishi, Tesla) specially exclude capacity from their warranty, which then largely covers only outright failure of the battery, not loss of capacity and hence reduced vehicle range.
You should be aware of these exclusions when you consider the purchase of any electric car.
And if you think your usage may be particularly harsh or you will regularly deplete the battery entirely and/or frequently fast-charge it, a capacity warranty may be a very good idea.
At the very least, comparison of battery warranties among different plug-in electric vehicles you may be considering should be a core part of your overall comparisons among models you're assessing.
Remember also that batteries, like human beings, prefer to stay as close as possible to constant temperatures around 70 degrees F, while higher temperatures will cause them to degrade more quickly.
Thus far, electric cars with liquid-conditioned batteries (e.g. Chevy, Tesla) seem to hold their capacity better than those with passive air cooling (e.g. Nissan).