ELI5 Batteries - what causes lithium batteries to degrade?

Are there ways we can slow the degradation of our smartphone batteries? Why does it seem like a wireless house phone battery can last for many more years than a smartphone battery? Why do traditional cars lack any decent ability to warn the driver that the battery is low or about to die? Why does hitting a flashlight when the batteries are low keep it working for a short time?

 

... We explain like i'm five!

 

Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: just_isaac, llevin5, steve204, crazy_eric, branden798, biff64gc, victorziblis, redol1963, logically_hindered, apatharas & sheppenwolf

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