A General Motors patent application addresses one of the downsides of electric vehicles--battery degradation--with a system that would let technicians refurbish a lithium ion car battery.

The patent application, submitted a year ago and spotted by GM-Volt.com, would be something like the electric auto equivalent of scheduled maintenance.

The lithium ion battery pack inside the Chevy Volt.

After several years of driving, the lithium ion batteries would either be refurbished on site or the battery pack would be swapped out. Even if a fresh battery pack is installed, GM's patent application argues that refreshing used batteries without totally dismantling them can save on costs significantly.

"The lithium ion battery may be removed from the vehicle and replaced with a new or rejuvenated lithium ion battery, while the removed lithium ion battery may be restored for subsequent use, thus saving vehicle owners and manufactures substantial costs normally associated with replacement and/or warranties," according to the patent application summary.

Like all rechargeable batteries, the lithium ion batteries used in the Chevy Volt, Nissan Leaf, and other electric vehicles coming to market degrade over time. These cars will continue to run but the range they can travel on a charge is expected to be impacted over time. Auto industry executives say to expect a 20 percent to 30 percent drop in range over 8 to 10 years.

GM's patent application calls for replacing the active material within batteries with a multistep process of inserting and removing existing chemicals. It describes a manifold and tubes that connect to "pouch-type" lithium ion batteries.

The idea is to insert a solvent to remove contaminants, such as manganese, from cells and to replace the liquid electrolyte in the battery. Then valves connected to the tubes would push fresh electrolyte into the pouches. The patent application said the operation, which would require heating solvents, can be done in minutes rather the several hours.

GM apparently does not expect such a process would fully restore batteries, though. "The power and capacity loss associated with the SEI (solid electrode interphase) layer, as well as the decomposition of the liquid electrolyte, are thought to be at least partially reversible, and it has been found that a low power and capacity battery may be able to recover at least a portion of its power and capacity for further use," according to the patent application.

Even though there are few vehicles with lithium ion batteries on the road at this point, people in the auto and utility industries have been thinking about how to get the most of out these batteries, which are the most expensive component in electric vehicles. Electric car service company Better Place, for example, has structured its business around owning batteries and stations where they can be automatically swapped out.

Utilities and energy storage companies, meanwhile, expect that they can use used vehicle batteries for grid storage. Even with the degradation after years of driving, the batteries can be linked together to provide energy and power for certain applications.