The BMW i3 hatch is available as either a pure electric vehicle or with an optional range extender petrol engine. Like the setup used in the Holden Volt, the i3's petrol engine is there to top up the battery pack whenever it begins to run low.
Consumer Reports is currently performing a long-term test of a range extended i3. During a drive with range extender in operation, one of its testers noted that once on a hilly two-lane highway, as they were attempting to overtake a truck, power dropped off dramatically without warning.
With the prospect of on-coming traffic appearing, that's a frightening situation to be in.
Upon doing follow up tests, the US publication found that if the i3 was driven in a fairly steady state, with little chance for regenerative braking, the BMW's acceleration ability falls off alarmingly, with the 0-60mph (96km/h) dash taking anywhere between 27 and 40 seconds.
Under normal circumstances, the i3 takes nine seconds flat to complete that sprint with the petrol engine in action. In pure electric mode the i3 can complete the run in 7.5 seconds.
In response BMW USA said that a raft of changes are due, for both new and existing cars, from the second quarter of 2015, at least in the US. These include a charge state indicator for the battery, early warnings whenever there's a chance for a temporary loss of power, and more aggressive battery recharging whenever the navigation system knows that it's in a hilly area.
We're currently waiting to hear back from BMW Australia regarding the issue and its fix.