BMW i3 range extender has the little engine that could, testing shows

Energy can be depleted at rather inopportune times, but BMW is working on a fix

Published: October 09, 2014 03:00 PM

The electric BMW i3 we’re testing is the version that comes with a range extender—a small two-cylinder gasoline engine that fires up when the drive battery is near depletion, acting as a generator to keep the electric drive system running. Relying on that gas engine when the main battery is depleted works well in most cases, including high-speed steady cruising, but not, we’ve discovered, if you demand more of it.

Recently, one of our drivers tromped on the pedal to pass a truck on a hilly two-lane highway. The i3 began to lose power without warning, subjecting the driver to more exposure in the oncoming lane. It then recovered rather quickly upon coasting, which converts energy and uses it to fill the battery. But losing power just when you need it most is disconcerting to say the least.

Energy depleated during hill climb.

Read our BMW i3 first drive. And learn about another observation we made in "Beware tailgating a BMW i3."

Further tests revealed that after a prolonged use of the throttle with little or no speed varying and no gentle braking to regenerate energy to the battery, acceleration ability falls off dramatically. In that state, we measured a 0-60 mph acceleration time that ranged from 27 to 40 seconds—as opposed to 9 seconds in normal range extending mode.  For the record, when the car is running purely on electric power it sprints to 60 mph in 7.5 seconds.

BMW bills the i3 as a car suited for a mega metropolis and as such, with frequent speed variation, it is unlikely to wind up in a situation like this. But it would be nice to get a warning light regarding the reduced power, as one gets in the Tesla Model S and Toyota Prius.

Asked for a response, a BMW spokesman, Matthew Russell, said that an enhancement is coming in spring 2015 that will address our concern. It will include a battery state-of-charge indicator, an early alert prior to potentially experiencing a temporary loss of power, and a proactive boosting of the battery level based on the car’s navigation prior to encountering hilly terrain. This enhancement will also be available as a retrofit for existing i3 owners.

Gabe Shenhar

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