The National Highway Traffic Safety Administration is investigating Tesla over alleged battery defects that have reportedly led to fires in the Model S and Model X.

On Oct. 24, the agency sent a letter informing Tesla that it planned to open a defect petition requesting that "certain battery management system software updates" be evaluated in Model S and Model X vehicles sold between 2012 to 2019 in the United States. It also requested information about those updates, as well as details on consumer complaints, lawsuits, and claims related to the alleged defects.

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The petition was filed in September on behalf of a group of Tesla owners who want answers about a software update that came after a series of troubling incidents in which Tesla vehicles burst into flames. In April, for example, a Model S in Shanghai caught fire seemingly out of nowhere. The vehicle wasn't running or charging at the time.

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After another incident in a Hong Kong parking lot, Tesla issued the update, which limited the cars' charging capacity and, according to some salty owners, decreased the car's range. At the time, Tesla said the update was out of an "abundance of caution" but did not specify to what extent it related to the fires.

According to Car and Driver, which broke news of the letter on Friday, Tesla has until Nov. 29 to respond to the inquiry. If it doesn't, it could face over $100,000 in civil penalties.