The BMW i3 REX has largely been overshadowed by its full-electric counterpart but the model is back in the news for less than stellar reasons.

The BMW i3 REX has largely been overshadowed by its full-electric counterpart but the model is back in the news for less than a stellar reason.

During a recent test, Consumer Reports discovered a potential safety issue when the battery is almost depleted and the car is using its range-extending petrol engine.

According to the publication, one test driver was attempting to pass a truck on a "hilly two-lane highway" when the model suddenly began to lose power. As the magazine points out, being exposed to oncoming traffic and "losing power just when you need it most is disconcerting to say the least."

In follow up tests, the publication discovered that prolonged trips with little to no changes in speed and braking "dramatically" affect the car's ability to accelerate. Under these conditions, the i3 takes 27-40 seconds to accelerate from 0-60 mph instead of the usual 7.5 seconds when running on electricity alone.

When asked about the issues, BMW USA Product and Technology communications manager Matthew Russell said the company is working on a series of improvements that will be available next spring. They will reportedly include a battery state-of-charge indicator and an early warning system to alert drivers about a potential loss of power. More importantly, the update will proactively charge the battery before encountering hilly terrain.

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BMW i3 REX bombs with Consumer Reports, can experience a sudden loss of power