There are so many myths floating around the internet about the use of mobile and laptop batteries. Both devices use Li-ion batteries. Most can be squashed with a single click on google search, though some might appear logical.
Myth 1 “I’ve seen a TON of people saying stuff like “It will hurt the battery if you use your phone before charging it” and “You need to do a full charge/drain cycle” to protect your battery.”
Lithium-Polymer and Lithium Ion batteries don’t have memory effect. So you don’t have to discharge your phone completely before charging.
Although sometimes it is useful to completely discharge and the completely charge your battery at a go for the purpose of recalibration. Recalibrate whenever you feel like battery % isn’t being reported accurately by android. It falls very steeply at some levels and holds for long at certain other level.
Myth 2: An overcharge will kill your battery
With Lithium Ion, in fact, is actually very bad to do a full discharge and it will reduce the capacity of your battery. 4.2v is full charge for lithium ion/Lithium Polymer, and there is a protection circuit built into the battery somewhere around 2.4-2.7v. Once that threshold of discharge is reached, the battery will cut itself off to prevent even worse damage.
Hence, due to the protection circuit in the battery, it cannot be overcharged. Also a partial charge upto 80-90% will be better than a full discharge as it will result in less stress on the battery (although this might depend on whether your charger charges your battery to a stressful level at 100%).
Myth 3: Charging with USB will have very adverse effect on your battery.
As a result of point 1, no need to worry about charging your phone by USB. It won’t have any adverse effects on battery life.
Myth 4: A full discharge will kill the battery
A full discharge once in a while won’t totally kill your battery, but it will reduce the recharge cycle life of the battery. Not a lot, but it will nonetheless.
Use always high quality or original chargers. Since it the charger which decides at what voltage the charging is being done. A local charger might do the job but the risk is still there. Li-Ion gets damaged if charged past 4.2-4.25 volts, and becomes an explosion risk should the internal vents fail. The problem with many cheap chargers is that they continue to slowly trickle charge past 4.2v. Hence, it will slowly rise to 4.21, 4.22, 4.23v. If you leave it overnight you very well may end up coming back to an overcharged battery that is not only holding reduced capacity from the damage, but is a safety risk as well.
P.S. You bought your phone to USE it. So don’t care too much about battery while using your phone. Batteries are dirt cheap these days.