General Motors announced on Thursday that it will install mechanisms to better protect the battery pack of its Chevy Volt electric-gas hybrid. GM stopped short of calling it a recall, but will notify customers of the more than 7,600 Volts currently on the road when the retrofit modifications are available although the company hasn't specified a time frame for this.

GM's action came in response to a federal investigation into the possibility that Chevy Volt batteries could catch fire during a severe side-impact collision. In May, the National Highway Traffic Safety Administration (NHTSA) crashed a Chevy Volt in a new car assessment program test designed to measure the vehicle's ability to protect occupants from injury in a side collision. During that test, the vehicle's battery was damaged and the coolant line was ruptured, according to the NHTSA. A fire involving the test vehicle occurred more than three weeks after it was crashed, and the agency concluded that the damage to the vehicle's lithium-ion battery during the crash test led to the fire.

The agency re-created the May test three times in November to better study what happened. In each of the battery tests, the Volt's battery was damaged and rotated to simulate a side-impact collision into a narrow object such as a tree or a pole followed by a rollover. Two of those tests resulted in battery fires, although none of the fires broke out immediately upon impact at the crash site. In one case, the flames started hours after the test. The other battery caught fire a week after it had been tested.

To reduce the likelihood of an electrical fire igniting days or weeks after a collision, the Volts will be fitted with steel reinforcements to the battery pack's existing safety cage. In addition, GM will add a sensor to the battery coolant system reservoir to monitor coolant levels. A tamper-resistant bracket will likewise be installed to the top of the battery coolant reservoir to help prevent potential coolant overfill. In addition to retrofitting Volts already on the road, GM said it would incorporate these additions into the Volt manufacturing process.

GM says it conducted four successful Volt crash tests in December after adding the structural enhancements. There was no intrusion into the battery pack and no coolant leakage in any of the tests, according to the company. A GM press statement indicates that, through the first 11 months of 2011, Volt owners accumulated nearly 20 million miles without an incident similar to the results in the NHTSA tests.

Images courtesy of General Motors