At $10,000 a piece, electric-car batteries are too expensive to throw out or recycle into scrap materials. And even after a decade of use, when they can't perform well enough to meet the vehicle's demands, they could still be valuable for other uses. Nissan and GM have both recently announced ways they might make some money from them.

Many issues remain unresolved, not the least of which is whether the automakers would need to buy back the batteries from car owners, or whether dealers would simply lease the battery rather than sell it, which would allow the car company to reclaim it for secondary uses later on.

This week, GM announced a new system that came from its partnership with power electronics and automation giant ABB. The system pairs a battery designed for the Chevrolet Volt with a commercial inverter for interfacing with the power grid. The system employs five to 10 used batteries and could provide a few hours of backup power for homes or small businesses. It could also be used by utilities to help keep the electrical grid working smoothly. Meanwhile, Nissan, as part of a joint venture with the Japanese industrial company Sumitomo, recently announced a system that uses solar panels to charge up batteries. The batteries could then be used to charge electric vehicles, such as the Nissan Leaf, even at night. The system already supplies power to seven charging stations at Nissan's headquarters in Japan, and the company plans to eventually sell smaller charging systems.