Select drivers in New York and New Jersey were given preview models of BMW‘s all-electric Mini E car and found that the battery’s charge lasted shorter than the company anticipated.

BMW owns the Mini Cooper brand and has developed an electric model of the car. Preliminary tests showed that the car was supposed to drive over 150 miles, according to the Wall Street Journal. However, those tests didn’t take into account real-world driving conditions, which, according to the drivers, have reduced the range by almost a third.

That could be bad news for claims made by automakers about electric batteries’ longevity. The Nissan Leaf, due out later this year, has a less-powerful battery pack than the Mini E and claims 100 miles, which is about what testers found the Mini E gets under real driving conditions. Nissan’s American product planner, Mark Perry, told the news source that the 100 miles depends on various factors, such as the weather and use of heating or air conditioning.

Until the battery issues are sorted out, drivers who still want to be environmentally-friendly might want to consider hybrid cars like the Toyota Prius. However, these cars can be expensive when bought new, so it might be best to look for deals on the used car market.