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Whats a battery lifespan? Is it capacity degradation or random failure?

If discovery slows down capacity degradation, but now your EV battery is 100x more likely spontaneously fail ($$$) - it's not really an improvement. Maybe ok for consumer device tho.

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There are two lifespans. The shelf life and the number of charge cycles (less of a span perhaps) where you charge to 100% and discharge to near 0. If you keep your charge/discharge to 80/20 then your battery life is limited primarily by the shelf life. eg. keep your Nissan Leaf in the 20-80% state of charge range and it will probably last 20 years, DC fast charge it every time to 100% you'll probably only get 2000 cycles (5-7 years) out of it.

It isn't that black and white, plus the Leaf without active battery temperature management isn't a representative example.

Modern Tesla's show fairly similar long-tail degradation that is nearly identical for cars that strictly home charge and those that only supercharge (based on customer vehicle tracking). Most will level off at 85-90% of original capacity.

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