It's one of the recurring questions asked by electric-car skeptics: Yeah, but what about all those battery packs? Won't they just end up in landfills?

We know already that the 12-Volt lead-acid car battery appears to be the most-recycled consumer good in the world--though that's largely for safety reasons, as lead is far more toxic than the materials in lithium-ion batteries. 

More recently, hybrid car-makers have had programs to take back and safely dispose of used or damaged high-voltage battery packs for 15 years. Those nickel-metal-hydride cells contain precious metals with a known recycling value.

DON'T MISS: Who Knew? A Car Battery Is the World's Most Recycled Product

But for the much higher-capacity lithium-ion batteries used in electric cars, the answers may be slightly different.

Lithium-ion battery pack for 2011 Chevrolet Volt

Lithium-ion battery pack for 2011 Chevrolet Volt

A new report from the Mineta Transportation Institute at San Jose State University in California suggests that 20 years hence, there may be 1.3 million to 6.7 million used battery packs from electric cars.

According to the report, as covered in Recycling International (via ChargedEVs), roughly 85 percent of those could be suitable for "post-vehicle use," with the remaining 15 percent likely damaged beyond repair.

There may not be a business model in recycling them, however: The materials in a lithium-ion battery pack are relatively inexpensive, and even with technological breakthroughs, the report estimates that only 20 percent of the cost of recycling could be recouped by selling the recovered materials.

Instead, the value will lie in secondary uses--depending, of course, on what value the market assigns to a used pack.

The report suggests that while this area is "less well-defined," repurposing the packs for other uses could be economical at a cost of $83 to $114 per kilowatt-hour.

Lithium-ion battery pack of 2011 Nissan Leaf, showing cells assembled into modules

Lithium-ion battery pack of 2011 Nissan Leaf, showing cells assembled into modules

For a 24-kWh used pack out of a Nissan Leaf, then, the value might range from $2,000 to $2,750.

The replacement cost of a new Leaf pack (on which Nissan has said it loses money today) is $5,500, assuming the old pack is turned back to Nissan (and the electric-car maker has its own plans for secondary-use businesses as well).

ALSO SEE: Nissan Leaf $5,500 Battery Replacement Loses Money, Company Admits

One potential application might be bundling a used electric-car battery with photovoltaic solar panels for home use, allowing homeowners not only to generate renewable electricity but to store it.

The average U.S. home uses 32 kWh a day, so a Leaf battery pack that may have 16 kWh of usable capacity left could power the home for a substantial portion of its day.

And forward-looking electric utilities are considering the opportunities to decouple such homes from the grid temporarily during periods of peak demand, reducing the utility's peak load.

Photovoltaic solar panels on roof of Honda Smart Home at UC-Davis, California

Photovoltaic solar panels on roof of Honda Smart Home at UC-Davis, California

One thing is certain, however: As Nissan is already doing, every maker of plug-in electric cars will have a program to take back used or damaged battery packs.

Some of them will see the value in repairing them--replacing defective modules and putting them back into stock as remanufactured parts--while others may set up separate businesses to sell them for secondary uses.

Which means it's only a matter of time until a "black market" emerges. Psst, buddy: Wanna buy a used electric-car battery?


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