Top US automaker General Motors on Thursday announced plans to reinforce the battery in its electric Chevy Volt in order to prevent fires after a severe crash.

The fix comes in response to a government safety probe launched after a damaged lithium battery in a Volt caught fire three weeks after a crash test.

Two other batteries caught fire in subsequent tests in which regulators intentionally damaged the battery compartment and broke its coolant line.

While there have been no reports of fires outside of government testing facilities, the probe called into question the safety of electric vehicles at a time when consumers are just beginning to consider them as an alternative.

"The Volt has always been safe to drive. Now, we will go the extra mile to ensure our customers' peace of mind in the days and weeks following a severe crash," Mary Barra, GM senior vice president of global product development, said in a statement.

GM dealers will reinforce an existing portion of the Volt's safety structure to better protect the battery pack, add a sensor in the reservoir to monitor coolant levels, and add a tamper-resistant bracket to prevent coolant overfill.

"These enhancements and modifications will address the concerns raised by the severe crash tests," Barra said.

"There are no changes to the Volt battery pack or cell chemistry as a result of these actions. We have tested the Volt's battery system for more than 285,000 hours, or 25 years, of operation. We're as confident as ever that the cell design is among the safest on the market."

GM's solution appears to work, the National Highway Traffic Safety Administration said in a statement.

The safety regulator said its testing showed that a fire is only possible when the battery is smashed and coolant has leaked.

It crash-tested a retrofitted Volt and found that the new steel reinforcement protected the battery and prevented coolant leakage.

"As a precaution, NHTSA has monitored the crashed vehicle since the test and will continue to do so for one more week," the agency said.

"However, the preliminary results of the crash test indicate the remedy proposed by General Motors today should address the issue of battery intrusion."

Volt customers will be contacted to bring their cars into dealerships beginning in February for the free fix.