Based on an exhaustive list of accolades, automotive experts and consumers have spoken: Tesla's (NASDAQ:TSLA) Model S is the best car ever built. But a few battery fires that occurred last year from high-speed impacts had investors worried that even the world's best car could be subject to a recall. Today, however, investors can rest easy. Tesla has addressed the issue of battery fires by adding a titanium underbody shield and aluminum deflector plates to the quarter-inch ballistic-grade aluminum armor plate that already protected the battery pack.

Tesla Model S. Source: Tesla Twitter feed.

The technology
Tesla CEO Elon Musk took to Medium, a new social blogging platform founded by Twitter co-founder Evan Williams, to explain the new underbody protection.

The new battery pack protection consists of three layers. The first layer, a rounded, hollow aluminum bar, is designed to deflect debris. The second layer, a titanium plate, "which has exceptional strength-to-weight properties and is more commonly seen in aerospace or military applications," is designed to prevent damage. The third layer aims to eliminate any risk of penetration whatsoever.

"By this point, the vast majority of objects will have been deflected or crushed. For the rare piece of debris that remains intact, we added a third shield, which is a shallow angle, solid aluminum extrusion that further absorbs impact energy, provides another layer of deflection and finally causes the Model S to ramp up and over the object if it is essentially incompressible and immovable."

The new shield prevented battery penetration in 152 vehicle tests performed by the company. In fact, in some of the tests the underbody objects never made it to the existing layer already protecting the Model S' battery. Tesla went to extreme measures to inflict damage to the underbody, claiming it tried every worst-case debris impact it could think of. Musk described one of the extreme scenarios, saying it included "hardened steel structures set in the ideal position for a piking event, essentially equivalent to driving a car at highway speed into a steel spear braced on the tarmac." Musk says the impacts on driving are small, having a 0.1% on range and no effect on driving or handling.

All cars manufactured after March 6 have been outfitted with the underbody protection. Further, any owner can get the shield added to the battery upon request "as part of a normally scheduled service."

Why Tesla needed to go the extra mile
The Model S was already five times less likely to catch fire than the average gasoline car based on current statistics. Notably, however, there hasn't been any reported Tesla battery fires since the company sent an over-the-air update to boost the default ground clearance of the Model S at highway speeds. Even more, the National Highway Traffic Safety Administration has given the car a perfect five-star rating in every category and no serious injuries or deaths have been reported so far.

But adding further protection was a necessary step for Tesla. Not only does it effectively address public misconception of the safety of electric vehicles, but it also reduces the risk of a recall. Since it currently produces just one vehicle, a recall is a major threat to Tesla. Not only would it be a financial setback for the company, but it would also hamper its incredibly important public image. Investors seem to be pleased. The stock rose about 2.5% on Friday.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.