Typical life of EV batteries

When EVs (electric vehicles) with Li-ion batteries first came out, one of the main things people thought would be a potential problem was that the batteries would need to be replaced periodically. They would cost a couple-three thousand or so, so it would be a significant expense. The usual estimate in those days was they’d last about 10 years.

Well, it’s now about 10 years since the first modern EVs were sold. I read a couple news sites about EVs and there’s no stories about replacing batteries. The only thing I’ve seen about this is some vague statements that batteries are lasting longer than expected. So do we have any idea how long EV batteries will last?

I have seen quite a few stories. Here is one.

I read that the information the EV driver sees on his instruments is not actually true, because the cells last a lot longer if not fully charged or discharged.

Apart from charge/discharge cycles, there are many other factors influencing battery life; notably temperature and how often ‘fast-charge’ is used.

That may be true for an electric rasor, but certainly not for a smartphone or a car with a lithium-ion battery. These batteries need a safety margin at both ends. Manufacturers are aware that people will typically recharge them every day, empty or not. Well-designed devices will manage this transparently; you can leave it plugged in for 8 hours if you want, but it will stop charging when the battery is around 80% of physical capacity.

This article from 2016 claims that no Chevrolet Volt batteries had been replaced due to degradation, but the car had only been on the market for about 5 years at that point.

Apparently, the battery pack in a Nissan Leaf can degrade because it doesn’t have a cooling system. Also, on the Leaf, the user can choose to override the charge safety margins (charge it beyond 80%, etc.). Which makes some sense because it’s an all-electric car with a relatively small battery pack, so sometimes you need to squeeze a few extra km out of it; but it will degrade the battery faster.

We actually have a rough idea. For the type of batteries they use, the battery will be down to 80% of the original capacity if you cycle them from 100% charge to 0% charge repeatedly approximately 1000 times. You can do this somewhere closer to 2000 times for cycles between 30% and 80%, which is the default setting for Teslas.

Note that there are other variables. Batteries age, and if they are near full charge they age much faster, without cycling. Batteries also are damaged by high charge rates (like DC fast charging, called supercharging by Tesla)

So a good guess might be 2000 * half the battery capacity = life in miles.

So with the new Tesla medium range model 3, which has a capacity of 260 miles, that would be 130 * 2000. 260,000 miles. But it might fail at half that if you drove very little (so calendar aging dominates) or supercharged often and also told the car to charge to 100% state of charge often.

Similarly, if you were to drive the car very often but not charge it over 70-80%, and kept driving it after the capacity is down to 80%, you might experience total battery failure somewhere over between 300k-400k miles. (once the capacity gets below 80% the rate of failure accelerates greatly)

This is a major concern primarily because the batteries are hugely expensive. Including labor the replace it, and it could easily be 12-15k. Essentially battery failure on an EV probably totals the car, for a vehicle like a model 3 that only sold at 40k, the depreciated value at the point the battery fails would be less than the cost of replacing the battery.

Guess I can’t afford a Tesla just yet.

People have made graphs.

Eyeballing the trendline, there’s a relatively quick drop to 95% capacity in the first ~40k miles, but then a much slower drop after that point. There aren’t that many data points on the right hand side, but it does look like 90+% capacity at 140k miles is not hard to achieve.

And note that this is the Model S, Tesla’s oldest model, and will include samples from early-run vehicles and also those for which the charge controller wasn’t entirely dialed in yet. It’s too early in the Model 3 history to have much hard data, but it’s likely that it will do better than the S since it will have incorporated all its lessons.

Tesla seems to be unique in giving less safety margin on the top end, and allowing the user to choose a balance between battery lifetime and capacity. They recommend charging to 80-90% on a daily basis, and saving the 100% charge for long trips. Since long trips are less frequent than commutes, this works well–you don’t incur much extra degradation if you’re only charging to 100% a handful of times a year.

Also, the degradation is something that happens over time–if you charge to 100%, and then drive it down to <90% immediately, the battery hardly suffers at all. It’s only charging to 100% and leaving it for long periods that’s a problem.

Well, I guess I read a different set of EV news sites. I certainly don’t read that one, but I’ll keep an eye on it in the future.

Sounds like a commuter who only occasionally makes long trips, keeps the car in the garage, and recharges at home with low voltage should have optimal battery life. Probably significantly more than 10 years.

If a battery lasts >10 years and 300,000 miles, I suspect that the main problem will not be buying a new battery, but disposing of the old one in an environmentally safe manner.

This is true of almost all Li-ion batteries, one may never, outside a lab, get a Li-ion battery that goes true 100 to true 0 because at the extremes of charge (near 100 and near 0%) the battery will have a much shorter life. So the info on the car’s dash, and your cell phone and air pods, and just about everything, except perhaps life safety devices which will go to true zero if needed, will have limits imposed. The stricter the limits the longer the battery will last but also the less run time you will get per charge.

Heat and length of time at all particulars state of charge are the largest factors, cycle life is much more of a hold over from other battery types where that was a good measurement of battery life for that type fo chemistry. It really does not directly apply to Li-ion type batteries (though is a holdover industry standard and why we use it).

I think the battery aftermarket replacement battery industry is still too new to answer the question of the long term life of EV’s. There are some places where battery packs will be disassembled and the weak cells taken out and replaced with those who test good.

In looking at the cites and other sources, I’m struck by how often “recycling EV batteries” actually means “retasking used EV batteries.” Kanicbird even mentions swapping out bad cells.

What is so hard about actually recycling (through complete disassembly and/or destruction) Li-ion batteries? It’s pretty easy to recycle the lead and other materials in a standard lead-acid car battery…if the economics make sense. Why is this not an option for Li-ion battery sets? If no effective method of doing this currently exists, who’s working on it?

It’s not hard. Electronics stores often have bins where you can deposit li-ion batteries for recycling. It’s just that used EV batteries are more valuable as batteries than as raw material. Reduce > reuse > recycle.

EV batteries that have degraded so much they no longer work as an EV battery have a secondary market as storage for wind and solar power. No reason to recycle something that still has value as-is. When it finally dies completely Li-Ion batteries are fairly easy to recycle.

I also think it’s a mistake to think that ‘once the EV battery is worn out you have to buy a new one at $15K totaling the car’. Many ICE engines cost $10k to over $20K but who’d spend $20K putting a brand new engine into a 15 year old ICE car? You’d just get a decent one from the junk yard. Same with a 15 year old EV, get a battery from a crashed car.

I would hope battery technology would improve a lot and the prices come down substantially by the time they need to be replaced.

We are still at an early phase and there are a lot of battery manufacturing plants about to ramp up production. At the moment the supply of EVs is restricted to small numbers by industry standards. So most EVs are sold at a premium.

The battery price is about $200 per KWh at the moment and falling. There are lots of guesses were it will be in 10years.

Without 10 years of data for EVs rather than hybrids, no-one can be sure how long they will last. There can only be educated guesses.