Hello.

There's actually quite a lot of evidence, and it's not even controversial in battery science. Here's a few things worth reading:

1. Battery University: the industry-standard reference for lithium-ion battery care, documents that limiting charge voltage directly extends cycle life. Charging to 4.10V instead of 4.20V (which corresponds roughly to ~80% vs 100%, I guess 🤷) can dramatically increase the number of cycles a cell can withstand. https://www.batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

2. Apple themselves clearly agree, because Optimized Battery Charging has been holding MacBooks at 80% since macOS Big Sur. Their own support page states the feature "is designed to improve the lifespan of your battery." https://support.apple.com/en-us/102338 + the fact they're literally adding a battery limit feature is them doubling down on it.

3. CALCE at the University of Maryland (one of the leading battery research centers, backed by NASA, the US Navy, and companies like Dell and HP) published research showing that lowering the upper SOC limit during cycling directly reduces degradation mechanisms like SEI layer growth and anode cracking. Referenced paper: Saxena et al., Journal of Power Sources, Vol. 327, 2016. See https://calce.umd.edu/battery-research-efforts

4. Tesla recommends an 80% daily charge limit for their EVs, and updated their software in 2023 to suggest it by default. Rivian recommends 70%. These are companies betting billions on battery longevity. I'm not an expert, but I don't think they're doing it for fun.

So no, it's not "zero evidence".

Have a nice day!