Many confusing and contradictory rules are shared about what smart phone users should do in order to keep a battery in good health. But just one need be remembered: smart phone batteries last longer if they aren’t completely drained before charging. Similarly, the Lithium batteries used in most modern smart phones don’t always have to be fully charged to 100%, according to advice from the German Federal Environment Agency (UBA). Unlike older generations of batteries, the lithium variety have no memory effect, meaning there’s no need to fully empty them before charging again. This means they don’t lose usable capacity if they are recharged repeatedly after being only partially discharged – as used to be the case with older nickel batteries. In layman’s terms, this simply means that if we charge our phones before they reach 0% and if we remove them from the charger before they reach 100%, it does not affect the durability and life of the battery. If batteries are left unused for an extended period of time, it’s best to store them at room temperature at a charge level of 40% to 60%.
Source – https://www.thestar.com.my/tech/tech-news/2018/04/14/how-to-keep-your-smartphone-battery-in-prime-condition/#g00i3RdjjWiKpGp1.99