What is the average shelf life of a new-in-box, never used Lithium-Ion cell phone battery?
Does the usefulness of such a battery degrade slowly over time, or does it just suddenly go from 100% to useless one day?
Most Lithium-ion batteries degrade over 5-10 years whether they are used or not. This degradation is a reduction in capacity, so a “new” battery that’s been sitting on a shelf for three years may only be capable of storing 50% of it’s rated charge.