BMW i, the luxury car maker's plug-in electric vehicle sub-brand, wants to use old i3 batteries for home energy purposes.

The program, announced during this week's Electric Vehicle Symposium in Montreal, repurposes high-voltage batteries, stretching a few more years of service from the retired power sources. It integrates with existing charging stations and solar panels to offset peak energy costs and provide backup energy supply during power outages.

As the program gets started, it will use new BMW i3 high-voltage batteries, but it will expand to include recycled ones as they become available.

"The remarkable advantage for BMW customers in using BMW i3 batteries as a plug-and-play storage application is the ability to tap into an alternative resource for residential and commercial backup power, thus using renewable energy much more efficiently, and enabling additional revenues from the energy market," Cliff Fietzek, manager of Connected eMobility for BMW North America, said in a statement.

BMW says the system is "ideally sized" for placement in a basement or garage.

"With a battery storage system electrified by BMW i, our customers can take the next step towards a sustainable energy lifestyle," said Rob Healey, manager of EV Infrastructure for BMW North America. "Coupled with the home charging and solar energy programs, the system enables BMW drivers to embrace holistic sustainability beyond e-mobility."

A typical US household averages 15 to 30 kWh of daily electricity (based on a 2014 report by the Energy Information Administration), so even a weakened i3 battery can keep the lights on for up to 24 hours, according to BMW.