Tesla batteries are the most expensive thing in a Tesla. This also has a lot of warranties, to learn more about their warranty you can go to tesla's website to learn more, but these are very well covered and prepared and to drive a long time. However some have shown that the battery can shut down or not hold it's actual charge. Tesla has prepared for this and will warn you in advance so you don't end up on a trip with a dead battery. In many cases they will warn you well in advance so there's no error which can be frustrating if you're thinking you want to go really fast because the battery is influenced by your speed as well as how far you go.
"For example, some Tesla owners have reported that their battery functions at approximately 95 percent of its original ability after only 50,000 miles. Depending on the Tesla model, a 5 percent decrease in battery range could equate to around 20 miles less distance per charge when starting at 400 miles of range." -Article
