> After ten years of daily use a lithium battery will have lost 50% of its capacity

No it won't. If your degradation is that bad, you would have been able to replace the battery before the warranty was up. Most manufacturers are similar, but Tesla has a 70%/7 year battery warranty. Any battery that will hit 50% in 10 years would hit 70% in 7 years and you would have had it replaced.

And obviously Tesla sets the warranty at a level where it doesn't expect to replace many batteries.

I had a look at the warranty and it says that they will not install a new battery, just one that gets you to the minimum of the promised degradation range:

  > For warranty claims specific to Battery capacity, the replacement Battery will be in a condition appropriate to the age and mileage of the vehicle sufficient to achieve or exceed the minimum Battery capacity for the remainder of the warranty period of the original Battery. Note that the vehicle’s range estimates are an imperfect measure of Battery capacity because they are affected by additional factors separate from Battery capacity. The measurement method used to determine Battery capacity, and the decision of whether to repair, replace, or provide reconditioned or remanufactured parts, and the condition of any such replaced, reconditioned or remanufactured parts, are at the sole discretion of Tesla.

https://www.tesla.com/sites/default/files/downloads/Model_3_...

Batteries tend to degrade to around 80% and then stay there. This is apparently the generally accepted trend now, but my anecdotal evidence matches: my Leaf is now nine years old and still has just over 80% of its capacity left.

I drive a LEAF, one of the absolute worst EVs in terms of battery degradation.

After 9 years and 1 month, my battery is down about 13% from new. 50% loss in 10 years is pure FUD, IMO.