The average electric vehicle battery is expected to last about eight to ten years, at which point they need to be swapped out for a new one. After the 10 year mark, EV batteries still have about 70 percent of their capacity, which means that even if they're not suitable for powering a car anymore, they're definitely suitable for other uses. As more electric vehicles are making their way to the road, the question of what to do with those used batteries when the time comes is becoming more pressing.

Renault, like other car companies, provides the batteries to car owners on a rental basis, so that when it's time to exchange the old battery for a new one, the company gets the old one back. Renault says that it has 120,000 EVs on the road already, which means it owns that many batteries that will be making their way back to the company in just a few years. What's a company to do with so many used batteries?

Renault has come up with a way to recycle the batteries in a way that will give them a new revenue stream but also continue to help cut down on fossil fuels. The company has partnered with home energy storage company Powervault to use its old batteries in home energy systems that store renewable energy from solar panels and let home owners use renewable power throughout the day, not just when the sun is shining.

Using the used batteries in the storage systems will bring down their costs by 30 percent, making them more attainable for a greater amount of home owners.

Renault will be conducting a trial of the Powervault units with its recycled batteries in 50 homes that already have solar panels installed. The testing will ensure that the performance is not affected by using reclaimed batteries. If all goes well, the units could have a mass market roll out in just a few years.

Renault will not be the only company to take its batteries from the car to the home. Nissan has also been working on a way to transition its LEAF batteries into home energy storage units.