Although the battery on your smartphone is fully charged, it drains quickly. in some instances when the phone shows that the battery has 30% remaining, it shuts down immediately. what might be wrong?

There could be many reasons, but with the initial symptom which was observed of the battery discharging quickly than usual, it would mean that the battery is already faulty or maybe nearing its end of life. Taking care of battery can prolong its life, simply by not playing when charging, using qualified of your brand and not letting the charge go below 20-15% of its charge. For most smartphones nowadays, it uses lithium based battery which is proven to be to date the most ideal material for use in battery on electronic devices over its predecessor alkaline based. Mainly due to its high energy density and lower rate of localization and discharge.

so much for the extra points :