Battery prices continue to plummet and they are lasting a lot longer than originally predicted. Myself, I'd worry a lot more about needing to replace  one of the current crop of 10-speed automatics in a new vehicle. I've owned a Tesla for about four years and mine has 48,000 + miles on it. There is a battery degradation test available but I haven't run it because any incremental range loss it may have hasn't affected me. Performance seems to OK too. 1/4 mile 11.96 sec @ 121.87 and 0-60 @4.19 sec. That's just a dual motor grocery getter. There is a you-tuber in Fla. that drives a 3-motor Tesla sedan. He is still running 9.1 second 150 MPH times with his car. he has over 900 time slips at drag strips. 20,000 + miles and still running original tires. He has replaced one set of brake pads and a battery -- in the key fob. That's probably unnecessary because the car would work fine with either a phone as the key or the supplies key card.