[zootboy]

The world of lithium-ion battery chemistry is quite complicated, but in my experience, the top contributors to battery wear-out are, in decreasing order of severity:

- Charge cycles (including partial cycles, e.g. 100% -> 50% is half a charge cycle)

- Depth of discharge (deeper discharge cycles are worse)

- Extended periods in hot conditions (over 40 degrees Celsius)

- Extended periods of being held at 100% state of charge

In essence, your charging behavior dings the first two items: higher number of charge cycles, and deep discharge cycles. If your goal was battery longevity, keeping the phone plugged in as much of the time as possible would be the best strategy. Bonus points if your phone supports a "stop at 80%" mode, but still the winner even without this feature.

[publicmail]

I think another huge killer of lithium batteries is charging them when below freezing. I bet most phones probably wouldn’t allow it though - or at least would limit it.

[zootboy]

I left out things that a typical battery management system will prevent, like over/under charging, or operating outside safe temperature limits. But yes, charging a typical cell below 0 degrees Celsius will immediately and permanently damage it. Here's a ref with some details on why:

https://www.bonnenbatteries.com/lithium-battery-low-temperat...

Li-ion chemistries that are tolerant of charging at low temperatures are a subject of active research.