The battery pack comes from A123 Systems--the same pack used on the Volt--but Ampera has an additional driving mode called Battery 'Halten,' or Hold. Battery Hold mode allows drivers to use the gas engine to power the electric motors, even when the battery is charged. We can't do that in the Volt. The Volt first uses energy from the battery before moving on to gasoline.
With the extra Battery Hold drive mode, Ampera drivers can choose when to use battery power, often opting to save it for later on in their commutes. This works best when going into the city from the suburbs. Drivers can use gasoline on the way in and get 30 mpg while driving on the highway, but can then select battery mode when entering the city. City driving is best for the all-electric mode because of continuous stop-and-go traffic.
Cities with restricted zones, like the European low emissions zones, only allow vehicles like hybrids, EVs, or low-emission gas engines. So using the battery mode is best in these areas. Also, when driving on battery in London, there is no congestion charge in the city center. Battery Hold mode is at home in Europe.
The downside to Battery Hold mode can happen when it's not managed properly. Per mile it is cheaper, and greener, to drive on electricity. If a driver uses gas when going to the city, then doesn't use all of the battery's range before leaving, the trip was not as efficient as it could've been. With the Volt, the better energy (battery) is always prioritized.
So how successful is the Ampera in Europe? Representatives have stated that there are already over 7,000 orders for the Ampera. Opel is optimistic about reaching their sales goal of 10,000 units for 2012. Having a car with Battery Hold mode in cities with congestion fees can really make the car appealing. In London, fees are about $18 every time you drive into the congestion zone. Add that to high fuel prices and the Ampera looks like a very good way to save money and drive smart.