Re: The elephant in the room...
I have an 8-year-old car (a Mercedes E-Class) and it's still in excellent condition. A lot could go wrong and still not cost $5,000 to set right.
If it were an 8-year-old Tesla with a $XX,000 battery pack nearing end-of-life, then I'd be getting pretty nervous right about now. Even eBay wants several dollars each for good 18650 cells, and the Model S has 7,000 of them. About $20,000 even DIY soldering in the cells yourself. And then your car and house would burn to the ground because you did it wrong.
Like I wrote - 'The elephant in the room...'
It's hard to be 'Green' when the expensive cars have a built-in self-destruct timer.
Like I said before, if Musk has figured how to make Li-ion cells last for 15 years, then that itself is worthy of a Nobel Prize in Science.
He should get away from the 18650 form factor and start winding up some much larger cells. Make a few easier and cheaper sub-modules. Not thousands in a big expensive lump.