This is a type of confusing question because the amount of time that a 18650 li-ion battery can last is dependent on a lot of factors.
The volume of time they are used, how often they are recharged, and their overall care are all vital factors that play into the durability of your 18650 li-ion battery.
Charging and Discharging the Battery
The situation that causes a 18650 li-ion to die is the use, the act of charging and discharging the battery. The longevity of an original battery primarily depends on these two components.
As such, the amount of time peruses that the 18650 li-ion batteries is having its power drawn is, of course, to be considered.
For example, if you are a security guard in the nighttime and you use a flashlight for most of the night, you will be using more of a percentage of your battery and therefore charging it regularly than a person who just uses light for a few minutes a day to take their pet outside or just has one on hand for emergency use.
Charging Method of the Battery
All this leads to the next and important factor that defines your battery’s lifespan. The number of times the battery is charged.
When a battery is charged it moves negatively charged ions from one side of the cell, the cathode, to another side, the anode. It is discharging the battery that makes the contrast.
Every time that you plug your battery in to charge, you are decreasing its maximum power and capacity by a little bit.
The best method for gaining the maximum life from your battery is to use it until it is at about 50% and then recharge it.
Another point to remember is that rechargeable batteries, including 18650 li-ion batteries, gradually will drain on their own over time. It is only the nature of the chemical composition of rechargeable batteries.
All this means a few things. First, you do not need to leave the battery plugged in and charging all the time. If you have it continually plugged in, the battery is going to be continually moving ions from the cathode as soon as they return there from the anode.
The second thing is that you must make sure to “top off” your battery regularly even when it has not been used.