When a lithium ion battery reaches the point at which it can no longer be used in an electric car, it still has the potential to be used in other applications. But exactly what are the best uses for them

The U.S. government is backing a comprehensive study to determine just that, the National Renewable Energy Laboratory (NREL) announced Tuesday.

"To date, no one has comprehensively studied the feasibility, durability, and value of Li-ion batteries for second-use applications," NREL said in a statement.

The California Center for Sustainable Energy (CCSE) will lead the research project which will explore the best applications for used lithium ion batteries. Potential uses include employing used batteries as energy storage devices for variable electricity sources like wind and solar that could also tie in to the electric grid.

"The NREL award to the CCSE team leverages an ongoing UC Davis-CCSE-TSRC study funded by the California Energy Commission on the repurposing of used EV batteries for home energy storage. The total budget for the NREL-CCSE second use battery project is approximately $1.3 million with 51 percent of the funding coming from CCSE and its partners," according to NREL.

The group will also examine how lithium ion batteries might be better designed or manufactured to maximize their potential for second-life uses.

NREL's project is not just a technical study. Like many Department of Energy projects in recent years, a comprehensive study on the economic consequences will be conducted in tandem with the application research.

The team plans to investigate how a second-use system might be used to temper the expensive cost of electric cars and electric-car batteries in the U.S.

It might be economically viable, for example, to have a system where people or companies can give electric-car batteries over for second use, and obtain a refund or credit for the battery's remaining value. Such a system might lower the overall cost of a lithium ion car batteries for manufacturers and consumers.

In addition to researching all the possible uses for lithium ion batteries, the study will also include comprehensive testing to determine battery lifespan, as well as developing a standard for testing and determining battery life.