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.  

But how long the used batteries would last is still in question. The GM-ABB system is being designed to deliver 15 years of use for utilities who want backup energy storage, which can be used to smooth out fluctuations on the grid caused by the variability in power output from solar panels and wind turbines. Over the next few years, GM plans to extensively test the batteries, as well as the electronics that would connect the system to the grid. Pablo Valencia, GM senior manager for battery life-cycle management, says GM will add more battery cells than the system really needs as a way of ensuring that it can deliver adequate energy for 15 years. He thinks the system can last that long because most of the loss in energy capacity happens in the first few years, “then it levels off.”

According to battery researchers, as electrodes and electrolytes age, they undergo changes in structure and chemistry that can make their performance harder to predict. That’s one reason that warranties on electric-car batteries are limited to eight years. Although lab tests give researchers some idea of how long the batteries will last, no Volts have been on the road long enough to adequately test the batteries’ durability.

The economic benefits of reusing the batteries aren’t clear, either. Pamela Fletcher, global chief engineer for the Volt, says it’s too early to say which options GM might find viable. One challenge is that since the latest EVs just went on sale, their used batteries won’t be available in large numbers for eight to 10 years. If the cost of new batteries decreases significantly over that time, as expected, it will be harder for used batteries to compete. Although the used batteries will already have been paid for, there will still be costs involved: they’ll have to be removed from the cars and repackaged for grid use, and automakers may also need to pay the car owners for the batteries.