The science of smartphone batteries and how to keep them charged - The Washington Post
'... In fact, as the video [below] explains, you're better off keeping your battery right around a 50-percent sweet spot. As Eric Limer explained for Popular Mechanics, a lithium-ion battery's charge capacity is determined by how many lithium ions it can nestle into its two electrodes. As you go through charging cycles, these components degrade and hold fewer ions. Battery University recommends partial discharges, because it's more taxing on your phone's battery to start from zero. If you constantly drain it down to nothing, your battery will lose its capacity much more quickly.
But heat is the real lithium-ion killer. Heat speeds up all chemical reactions, and the ones inside your battery are no exception. Not only can heat speed up the process of battery drainage in the short term, but it can also cause the battery to degrade and hold fewer ions. Even the heat of your body is enough to help kill a battery quicker — so try to keep your phone out of your pockets.
And finally, if you need to put your phone away for a while and don't want it to die completely, charge it to around 50 percent before you turn it off. A battery with no charge can become unstable or even explode, so smartphones and laptops have a fail-safe that kills their batteries if they're uncharged for ages and ages. It's a pain in the neck, but it's better than a phone explosion.
...'https://www.washingtonpost.com/news/speaking-of-science/wp/2016/09/13/the-science-of-smartphone-batteries-and-how-to-keep-them-charged/How to Keep Your Phone Battery Charged Longer - YouTube https://www.youtube.com/watch?v=zUlbHMDCosI