Slowly developing consumer interest in electric vehicles has been attributed, primarily, to two obstacles; sticker shock and apprehension over limited mileage and battery range.

Nissan Motor Co now plans an independent investigation prompted by a small group of Leaf owners who believe their batteries are aging too fast, according to Lindsay Chappell of Automotive News.

The good news here is that Nissan is being proactive; it did not wait for NHTSA to intercede or ask for a recall. Instead it launched an investigation with an independent third-party. Former GM marketing manager Chelsea Sexton has agreed to form a worldwide group to investigate the problem independently of Nissan.

Chappell reports that only about 14,000 Leafs have been sold to U.S. consumers over the past two years, and in many cases to eager early adopters of electric cars who waited months to obtain their Leaf from Japan.

Nissan has repeatedly reminded buyers that -- as with cell phone batteries -- the car's lithium ion battery modules will lose their ability to hold a charge with age.

But Nissan maintains that they should still retain an 80 percent charging capacity after five years of use. Nonetheless, seven vocal Leaf owners in Phoenix have gotten the company's attention. Those owners, Chappell says, claim that their batteries are losing capacity after only a couple of years. "A squall has erupted on green-car websites among owners and alternative-vehicle enthusiasts who suspect Nissan is concealing a product flaw."

Nissan reportedly took the seven Leafs in question to its Arizona proving grounds to examine and test the vehicles. They concluded that the cars in question simply had higher-than-normal mileage.

High mileage or not, if those vehicles are less than five years old they probably shouldn't be losing charging capacity this soon, should they?