@kenjuma96 there's a website called battery university that'll answer all your questions.
What @kamonye said is somewhat accurate. The truth is that at higher charge levels, the internal resistance of a lithium-ion battery increases and that decreases longevity. According to battery university which has real scientists, a li-ion battery should be maintained at around 10% to 90% for maximum durability. Here's a link to that effect
@Lulu_Wambua, battery calibration is no longer necessary in newer versions of Android (after 4.4). The operating system does that automatically even if you don't manually clear batterystats.bin. After a few charges the percentage showing on your phone will be totally accurate without your intervention.
@aydensaruni look at the info on the link I provided. A battery's state of charge significantly affects its longevity. One more thing... Trickle charging only applies when the battery is almost full. Even then, playing games will decrease the battery level because it consumes more than the charger can provide. Also, the phone primarily uses charge from the battery. Basically, only the battery has a stable enough current for the phone to use so the phone takes out of the battery as the charger struggles to fill it. As a result, the extreme stress that the battery will be under at that time will significantly reduce it's life expectancy. Also, good luck keeping the temperature below 50 degrees Celsius at which point irreversible damage to the battery starts to occur.
What @RINYE says is being implemented in newer versions of Android because it increases the longevity of any lithium-based battery. If you look at the charge curve of a device running Android 6 or higher on a phone that is plugged in overnight, you'll notice that charging stops at around 90% and the final 10% is topped off just minutes before you wake up (next scheduled alarm.)
What @marcus254 said also supports the fact that a lithium-based battery should not be kept too empty or too full to make sure that internal resistance is kept at a minimum. This increases durability.