Keep in mind you wouldn't regularly fully discharge a car battery pack, however you would discharge a phone battery. Thus capacity reduction occurs at a slower rate than a laptop or phone.
Why don't electric car manufacturers build in some time-dependent margin into their range estimates?
E.g. Only display a range of 350 miles at the start of a battery pack's life even if the real range is 400 miles. To the user, the batter pack performance would appear static (to some limited lifetime, anyway). At the end of life the margin would be zero, and the actual life would be equal to the true battery capacity at that time.
I know Tesla and GM would much more happily report the new battery range than that of a tired, old pack...
Some do that. The Mercedes B-Class Electric is one example. Tesla is more "honest", so you actually get to see the full capacity.
This does mean that you can see the capacity very slowly decrease over months and years, but I would personally prefer to know what's actually happening and be able to get the maximum range out of my car that I can.
The trade off is that the mere option to have higher range up front actually increases the rate of degradation!
So, would you rather have high range first and low range after six years, or a motte even range that degrades more slowly and is better after the first few years?
I prefer the latter.
The yearly losses are fixed, unrelated to usage. The per-cycle losses are indeed less when you don't fully discharge, but only by a relatively small amount.
Lets say you have a battery with a capacity of 100. Empty it completely 100 times and the capacity might be around 95.
Empty it only 20% 500 times (for the same total energy usage) and it's capacity might have only degraded to 97.
Better, but not nearly enough to erase the other effects.
Table 2 shows the lifespan of a typical Lithium Ion battery based upon various discharge depths. 100% discharge rates degrade to less than 70% of original capacity after only 300-500 cycles.
25% discharges hit the same value after 2,000-2,500 cycles. That level of discharge is fairly common with cars like the Tesla.
Having said that, you do have a point about overbuilt batteries too. Some Teslas do have much bigger than rated batteries that are software limited. It is completely possible for someone else to "beat" them on range by utilizing more of the available capacity.
>25% discharges hit the same value after 2,000-2,500
This is exactly the point (and easy to miss)
The degredation per energy used is about the same.
1 cycle of 100% = 4 cycles of 25%
So the 300-500 cycle loss is equivalent to 500-625 when you divide the number of recharge cycles by 4. You _must_ do this for an apt comparison because what you should be interested in is how your capacity deacys with usage.
Artificially smaller capacities also means that using the supercharger is more common. Another feature of lithium battery chemistries is losing capacity faster at higher charge/discharge rates. Trickle charging overnight will cause significantly lower cycle decay than supercharging in an hour (or whatever period it is)
I'm not sure that I understand your point right now.
With 300-500 cycles at 100% utilization, a 300 mile car would have degraded its battery to 70% after 90,000 - 150,000 miles. With 2,000-2,500 cycles of 25%, the car would have traveled 150,000 to 187,500 cycles.
That seems like a significant improvement to me?
Your point about supercharging is similarly valid, but also a little misleading. The big factor there is temperature and the Tesla packs use active cooling to reduce the hit from more aggressive charging. I'm not sure that anyone has really seen a significant impact from this.
Basically, battery quality and management matter. Tesla does those things pretty well.
E.g. Only display a range of 350 miles at the start of a battery pack's life even if the real range is 400 miles. To the user, the batter pack performance would appear static (to some limited lifetime, anyway). At the end of life the margin would be zero, and the actual life would be equal to the true battery capacity at that time.
I know Tesla and GM would much more happily report the new battery range than that of a tired, old pack...