Tesla is just weeks away from introducing its much anticipated, lower-cost, longer-lasting battery for its fleet of electric vehicles.

The battery is said to be revealed at Tesla's 'battery day,' which is an event in which Musk plans to showcase a number of significant advances in battery and battery production technology from Tesla and its partners.

This new battery, dubbed the "million-mile" battery, is said to do exactly what it says on the tin – and that is to last in excess of a million miles before needing replacement.

Tesla is already leading the pack in terms of reliability; they offer an 8-year warranty on their Model 3 cars (up to 160,000 miles.) They also offer the guarantee that their batteries will maintain no less than 75% capacity under normal use.

So, why does Tesla need this new battery, and why is there so much buzz surrounding its announcement?