Well, Tesla will replace the battery under warranty for up 8 years/150K miles if it has less than 70% capacity. That means used Teslas in the 8 year old range would tend to have batteries with at least 70% capacity. To me that’s still a vehicle with some value. Even a vehicle with only 50% capacity could still be a used as an in-town commuter vehicle, it would seem.
The Tesla model 3 went on the market in 2018 so the oldest ones are around 5 years old now. I just checked eBay and the ones in that age range with around 100K miles seem to sell for $15K - $20K.
It’ll be interesting in the coming years to see how the market values EVs that have moderate loss of battery capacity. Will they be considered worthless bricks or will they still retain some value?
It’ll also be interesting to see how the falloff in battery capacity really works in the real world. Will it decline gradually to a certain level and then fall off a cliff? Or will it kind of level out so that it stays fairly constant for a number of years? Or will it decline steadily along a sloping line to zero?
There is LFP battery technology that addresses some of the battery degradation issues, but there pros and cons. Here is a article that explains them. Looks like Tesla is going live with LFP batteries for standard range batteries.
https://www.recurrentauto.com/research/lfp-battery-in-your-next-ev-tesla-and-others-say-yes
It would seem so... I can tell you judging from my own fairly lengthy experience with lithium based batteries, once they get down to the 50% range they can crap out on you completely at almost any time. They do not typically linger for very long once they start to fail. And you also may end up with cells that start overheating and put the entire battery at risk.
People with skills, training and equipment can sometimes squeeze a little more life out of them, but this is typically more along the lines of adding sawdust to motor oil to hide a rod that is knocking or crankshaft that has main bearings that are shot.
This is one of the primary reasons China has junkyards filled with abandoned electric vehicles. Believe me they are more adept at using crap that is ready to be retired than people here are.