If you have purchased a Honda Civic because of its fuel economy and low emissions, you may want to think twice about getting a new software patch offered by the Japanese automaker. A recent letter mailed out to more than 100,000 owners of 2006-2008 Civics in the U.S. and Canada, warns owners that their batteries may deteriorate and eventually fail sooner than expected. They offer a free software patch that will prolong the life of the battery as well as improve performance, but many owners who have received the update, claim that it has made the car sluggish and reduced the vehicle's gas mileage. Hybrid owners fear that Honda has decided to sacrifice their vehicles' performance in order to avoid the huge cost of replacing faulty batteries.

The software updates have caught the attention of the California Air Resources Board, which regulates vehicle emissions. The agency met with Honda officials last week to determine whether the changes would increase emissions, a potential legal violation that could trigger a mandatory recall, fines or both.

The battery issue has also attracted the attention of plaintiffs' attorneys, who said they were considering adding it to existing legal claims that the Civic hybrid delivers lower gas mileage than advertised. Attorney Nicholas Chimicles of Haverford, Pa., said he was reviewing the new software update to see whether it has bearing on a suit he filed against Honda seeking class action status. That case, filed in 2007 and still pending, alleges that the advertised mileage ratings of the Civic hybrid proved unattainable in real-world driving. If that is caused by faulty batteries, he said, it could bolster his case.