[revelation]

Laptop and phone makers have pretty much zero incentive to protect the batteries they install.

The key to keep LiIon from degrading is 1) never allow it to go 100% full 2) never have it go 100% empty 3) avoid high battery temperatures, cooling if necessary.

Now on 1) and 2), to do that you have to give up battery capacity. If you only ever discharge to 5% and charge to 95% you've just given up on 10% of battery capacity. This makes your laptop look bad on "battery life" benchmarks.

For 3), as batteries make up 80% of the physical space in phones and laptops, that makes it very difficult to cool them actively or otherwise effectively. At the same time manufacturers want to sell fast charging capability to customers, and that's perfectly fine with LiIon, most of them are capable of gulping up much more current than most chargers deliver, only this dramatically increases the heat buildup in the battery. That's fine for a Tesla as it has liquid cooling for individual cells, but phones or laptops have none of that.