Often when getting an answer how long a battery will survive you get the answer how many loading cycles it will survive. But, what is a charging cycle? From 0 to 100% or also from 80 to 100%? My guess would be, that you have to sum it up. But how does regeneration affect the life span? Is it like a little loading cycle which reduces the lifespan? So, would the battery live longer if you could switch regeneration of and use it only on longer trips where you would longer range?

According to Battery University: The cooling system on the Roadster (and Model S) keeps the pack at a pretty consistent temperature so the elevated temperature isn't an issue (unless you use Performance mode too often). Battery University considers the "End-of-life" when a cell can't hold more than 70% of it's original capacity. They did a charge/discharge test on Lithium-Ion batteries and found that a 10% discharge resulted in 4700 cycles (before a battery will only charge to 70% of it's original capacity). A 25% discharge resulted in 2500 cycles, 50% discharge resulted in 1500 cycles and a 100% discharge resulted in just 500 cycles. So, if regen usage results in less depth of discharge for the pack then it would improve the pack's useful lifetime. I'm not sure how much of that is applicable to Tesla's pack but figured it would be worth mentioning.

Do the math on those numbers and they suggest that 50% discharge is your best value in terms of usable energy. 0.10 * 4700 = 470 0.25 * 2500 = 625 0.50 * 1500 = 750 1.00 * 500 = 500 Can you provide a reference? It would be very interesting to see the results of a slightly different experiment: 1) 10% charge where you discharge from 85% to 75% and then recharge to 85% 2) 25% charge where you discharge from 85% to 60% and then recharge to 85% 3) 50% charge where you discharge from 85% to 35% and then recharge to 85% 2) 85% charge where you discharge from 85% to 0% and then recharge to 85%

The % discharge doesn't tell the whole story either. Where that percent resides also matters a lot. For example for 10% it can be any of the following (plus even more granularity like 89-99%, but I'm going by tens for easy math): 90-100% 80-90% 70-80% ...etc. In general it would be best to stay away from the two extremes (100% and 0%).

You are absolutely right. Stay away from the extremes - ie Range Mode, and depleting your pack down to nothing - which EVERYONE knows they shouldn't do!! The life of your pack depends on where you live such as ambient temperatures, how you use and charge it, etc. The equations are a "general" experiment and do not relate to real world applications.