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Comment by alanh | Hacker News Reader

what is 'state of charge swing'?

I think it is referring to the fact that it is ubiquitous to leave some amount of reserve so that the battery is never fully charged (100% SoC) or discharged (0% SoC). This formulation is capable of going the full 0-100%, while most formulations will last significantly longer if they don't do that.[1] In that graph, charging to 75% and discharging to 25% gives you about 3x more life than from 25%-100%.

NB that most li-ion cells are rated for 300-1000 cycles at 100% Depth of Discharge. Reducing the DoD to 90% or 80% will get you thousands or tens of thousands of cycles, although it is abnormal to actually measure that long. A charge-discharge cycle at .1 C (the former standard) takes 20 hours.

[1]: https://batteryuniversity.com/_img/content/DST-cycles-web2.j...

24kw leaf battery is an example of this with user stats seemingly bearing it out. Charge it to 80% each time, you can expect 3000 cycles before it's spent (drops below 85% of original capacity). If you charge to 100% each time, you'll only get 1000 cycles.

3-4 years versus 8-10 years use makes a big difference.

The 85% capacity benchmark seems pretty arbitrary to me. I'd imagine most owners very rarely use more than 85% of their range (or at least, could avoid doing so easily) at which point 85% isn't "needs expensive battery replacement", it's just "slightly less range buffer". I imagine in 20 years' time we'll see plenty of old beaters, student cars etc. with 50% or less range that are still quite happily driving around.

That's already the case, you can pick up 2013 Nissan Leafs with very small batteries for small money. They're used for commute cars or grocery pickup.

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