Tesla Adds Battery Shields, Ending U.S. Fire Probe

Tesla Motors Inc. has added three underbody shields to protect the battery of its Model S electric sedan from road debris.

Separately, the National Highway Traffic Safety Administration dropped its probe into two battery fires in Tesla cars that ran over debris after saying it found no "defect trend."

The company began installing the shields in cars produced after March 5 and will retrofit them at no cost to owners of Model S cars built earlier. Tesla earlier remotely reprogrammed suspension control software to give the Model S a slightly higher ride height at highway speeds.

CEO Elon Musk announced the new shields and posted videos showing them deflecting or crushing such items as a trailer hitch, concrete block and engine alternator.

The three-part protection package includes a hollow aluminum tube intended to deflect debris or, in the case of an extremely rigid object, tumble it so it pikes into the underbody ahead of the battery pack.

Aft of the tube is a titanium plate to shield underbody components near the front of the car. Positioned further aft is an aluminum extrusion designed to push the entire car up and over an object that gets past the first two shields.