“What happens to a Tesla battery after a few years of driving and charging? As you can see in the chart below, a new car starts off giving over 100% of the EPA range, but from there the battery does indeed deteriorate over time—however by seven years old the average Tesla battery still provides around 93% of its original capacity and range”.

This is fairly amazing for a battery:

Can you imagine your phone’s battery only losing 1% of capacity per year?

Yeah right.

Since battery capacity is more a function of distance driven (distance = recharge = decreasing capacity) than years, here’s a plot of that:

So at 196,000 miles (315,000 km), the trend line corresponds to a charge of 90%.

This would mean a remaining capacity of 50% after around a million miles (more than 1.5 million km).

For the average American, that works out to be 76 years of driving!

However, I would probably consider modeling with a polynomial curve rather than a straight line towards the right-hand side, as it seems to be curving down—i.e., a small acceleration in battery capacity loss. Probably less than 50% remaining after the first million.

At what remaining capacity does the battery become technically “useless”?

Probably depends on the user. If you never ever drive out of town, you’ll still be able to use a battery with 20% capacity remaining. But if you have frequent or occasional long trips to take, low remaining capacity will become a bummer at some point.

You can almost imagine an exchange market for people with different requirements for battery range at different points in their lives. However, Tesla currently doesn’t have swappable batteries, so you’d have to swap the car too, which might be awkward.

More details and plots can be found in this article.