An official range calculator for the Opel Ampera-e shows range slashed by 64 percent when driving in sub-zero temperatures with the heater on.

The Opel Ampera-e's driving range could vary by nearly 250 miles depending on driving conditions and other factors, according to an official range calculator. The finding raises concerns over cold-weather performance for the vehicle's US-market equivalent, the Chevrolet Bolt.

Opel's website features a dynamic range calculation tool that allows potential buyers to evaluate estimates based on expected average speed, ambient temperature and whether the heating and air conditioner are active.

All electric vehicles are prone to significant range degradation in cold weather, but Push EVs noticed the losses appear to be particularly extreme for the Ampera-e. If the driver is traveling slowly with the cabin heater enabled and it is -4 degrees Fahrenheit outside, they should not expect to cruise for more than 104 miles before the battery is depleted -- a 57 percent drop from its standard range estimate. Taken to the extreme, it is a 70 percent reduction from the peak 351-mile range for a low-speed run at 68F without the heater or AC running.

The tool is based on the Worldwide Harmonized Light Vehicle Testing Procedure, promoted as a more realistic method than the New European Driving Cycle. Opel expects the Ampera-e to have a WLTP combined range of 240 miles, nearly identical to the US EPA-estimated 238 miles for the Chevy Bolt.

Tesla also offers a dynamic range calculator for its current production vehicles. The Model S with a 75-kWh battery is expected to have its lowest range of 184 miles at 70 mph with the heat on at 0 degrees F, a 26 percent drop from its 249-mile EPA range estimate. The To be clear, Tesla is presumably not using the WTLP cycle and employs different speed and temperature ranges for its calculator.

With conflicting test cycles, it is impossible to conclude definitively that the Bolt is any worse than other EVs. The information does serve as a reminder that interior climate-control settings can be a potentially critical oversight when driving EVs near their range limits in extreme temperature conditions. If an Ampera-e driver is making a long-haul trip in sub-zero temperatures, simply leaving the heater off adds nearly 184 miles of range.