You do not have to calibrate anything. It is with that percentage, because they leave the devices a long time off, and it is so that the battery does not reach 0 until they are sold, because if it reaches 0 you have a completely dead battery.
These are not the batteries of 20 years ago.
Download it to below 5%, make it a full charge, and then try to be between 20% and 80% for the following ones, so that it lasts as long as possible and that the degradation is as slow as possible.
From time to time, every 3-4 months, you do a full discharge and recharge, to calibrate the battery.
That's all you need to know more or less.
The 20-80 is a reference, it does not have to be exact and nothing happens if you go above 80 or down to 20, just try to be as close as possible. If you forget loading or you forget and ends up downloading everything, well it is no tragedy.