The Nissan Leaf, easily the top-selling electric vehicle worldwide, is still working to overcome inherent disadvantages like long charging times, but the company is also adding an interesting new feature to its Japanese in-home charging stations. The "Leaf to Home" charger, which will start showing up in showrooms come mid-June, is a fast-charging power station about the size of an air conditioning unit. It's supposed to charge a Leaf in four hours, half the standard in-home charging time. Once installed, though, it doesn't simply transfer power from grid to car: it also turns the Leaf into a backup battery for the owner's home. Nissan estimates that the 24kWh stored in a fully-charged Leaf is enough to power a Japanese household for around two days, and conversion efficiency for storing and providing electricity is rated at 90 percent or higher.

Since the near future of Japan's electrical grid is still uncertain in the wake of the Fukushima disaster, the car battery could act as an impromptu generator in emergencies. In more mundane situations, Nissan suggests it could be used to store solar power or supply electricity during high-demand parts of the day, although we imagine it might be easier to simply invest in a separate battery after a point. The charging station will retail for 330,000 yen, or around $4,200 US; Nissan doesn't look to have any plans to sell it outside Japan but hopes to sell 10,000 units in-country this year.