[colechristensen]

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.

[_ea1k]

That assumption is actually incorrect. Data: http://batteryuniversity.com/learn/article/how_to_prolong_li...

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.

[colechristensen]

>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)

[_ea1k]

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.

[mynameisvlad]

I mean, even with your calculated numbers, it still shows 25% discharge gives back better results than 100% dicharge, based on the ranges alone.