After two separate battery fires, one the darling of YouTube, Tesla Motors Inc (NASDAQ:TSLA) announced today that it has added three underbody shields to the Model S in order to further protect the car’s batteries in the event of impact. Prior to the addition of the shields Tesla had swapped out the software that lowers and raises the car based on speed, opting for a higher default ground clearance.

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NHTSA closes investigation

Coincidentally, the National Highway Transportation Safety Agency also ended its investigation of the Model S following the two fires today without pushing for a recall that would have crushed the automakers’ (overvalued?) stock price.

Documents posted on the NHTSA web site revealed the reasons for the closed investigation and stated that the agency “believes impacts with road debris are normal and foreseeable. In this case, Tesla’s revision of vehicle ride height and addition of increased underbody protection should reduce both the frequency of underbody strikes and the resultant fire risk.”

The report read “a defect trend has not been identified. Accordingly, the investigation is closed.” It did however state, “The closing of the investigation does not constitute a finding by NHTSA that a safety-related defect does not exist, and the agency reserves the right to take further action if warranted by new circumstances.”

Musk comments

Responding to the report, Tesla Motors Inc (NASDAQ:TSLA) founder Elon Musk wrote on the company’s website “a few months ago to increase the default ground clearance of the Model S at highway speeds, substantially reducing the odds of a severe underbody impact.”

Musk also believes that raising the car solved the problem but wished to give owners extra insurance by adding the battery shields. He reiterated that Tesla Motors Inc (NASDAQ:TSLA) will not recall the Model S.

Tesla Motors Inc (NASDAQ:TSLA) is not recalling cars already on the road, but will “retrofit the shields, free of charge, to existing cars upon request or as part of a normally scheduled service,” Musk wrote.

Kelley Blue Book’s senior analyst, Karl Brauer, is of the opinion that the additions of plates and raising of the car will put the fire issue to bed, “Tesla has added substantial protective measures to the underbody of the Model S,” he said “This combination of upgraded materials should further reduce the chance of a battery pack puncture. Given that no punctures have been reported over the past 4 months, even without the added protection, this fix should eliminate the potential of a battery-pack fire under all but the most extreme circumstances.”