The BMW i3's range extender is now the subject of a lawsuit

When you buy a BMW i3 electric vehicle, you have the option to include a range-extending gas motor. The REx, as it's known in car-geek parlance, is a 34-horsepower, two-cylinder engine that provides juice to the battery to boost range from about 80 miles to somewhere around 150. But in certain conditions, engaging the REx can get...hairy, as one lawsuit alleges.

MLG Automotive Law filed a national class-action lawsuit against BMW's US arm over this REx. "[W]hen the gasoline engine kicks in, it doesn't produce enough power to prevent a dramatic decrease in the vehicle's performance," MLG wrote in a statement.

As our own editor Chris Paukert has experienced firsthand, it takes a special set of circumstances to create this decrease in power. Essentially, when you've got a heavy load (such as long uphill stretches or if the car's filled with passengers), the electric motor can't produce enough juice to keep the vehicle moving while the REx attempts to charge the battery. Thus, its net output is reduced to produce a net gain on charge, extending the vehicle's range.

The problem with this solution is that the car can cut its power at inopportune moments. So if it cuts off in the middle of a 70mph cruise, you could find yourself on a 55mph white-knuckle drive, surrounded by faster, bigger vehicles that are suddenly forced to pass you. For drivers not aware of this, it can come as quite the surprise. BMW spokesman Dave Buchko said the company cannot comment on pending litigation.

While it may not act as a panacea, the simplest solution to this is to have dealers better educate customers before deciding on a REx-equipped i3. It might turn a few people off the prospect of i3 ownership, but it would likely prevent future lawsuits along these lines.

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