How much do electric car batteries degrade?

Summary

It’s always the battery in my mobile phone that gives up on me first. After just a few years, it can barely make it through the day without getting another charge.Most electric cars have the same types of batteries — usually lithium-ion — so the assumption is that they degrade just as quickly. This is a fairly common fear for people considering a new EV: “Won’t the battery need to be replaced after a few years?”. And I think it’s even more prominent in the second-hand market: “Oh, I’d never buy a second-hand battery!”.But the types and structures of electric car and mobile phone batteries are not the same. Car batteries are designed to last far longer.A few months ago, I wrote about the fact that the electric versions of many cars were now cheaper than their petrol equivalents in the second-hand market. Most of the responses to that article suggested that battery degradation is the reason why. But looking at the data, I’d say that it’s more likely to be the perception of battery degradation that pushes the value down, not the actual degradation in reality. Pessimism about battery longevity is giving us all cheaper second-hand EVs, which is a nice perk for now, but not great if we want to see a widespread shift from petrol to electric. This is not the only reason I think used EVs are now undercutting the price of petrol cars; the fact that so many newer (and better) models are coming on the market means that many models — even just a few years old — lose some of their comparative value. Again, I think this is a pretty good thing (at least if you’re a prospective buyer).Anyway, let’s take a look at battery degradation: why it happens, how much EV batteries degrade, and how to reduce it.Two types of degradation happen in an electric car battery:First, calendar aging, which is when the battery loses capacity over time, even when the car isn’t being used. So if you were to have an electric car, and not touch it for a year, the battery would still experience small amounts...