1) leaving in charger all night is good or bad?
-That is fine. Also, to get the best charge, do not use your device while it is charging.
I find that turning on Airplane mode while it is charging helps, as well.
2) How to charge for the 1st time
Hear that i have to leave it for 8 hours on charger?
-Leave it on the charger until it is at 100%. It shouldn’t take 8 hours to fully charge it.
3) If it happened and i have to unplug it before it reached 100% ?
-Whenever you can connect your device to a charger, connect it and allow the device to fully charge. If you can’t in one setting, try to allow the device to charge overnight.
4) Is it good or bad for the battery to charge from 40%
-If it is a one time occurrence then that’s fine. However, you don’t want to get into the habit of doing that.
5) About powerbanks ??? is it good to charge from ?
-As long as it is a genuine Apple product made for your particular iPhone and your iOS is up to date, you can use it.
Make sure that it is an Apple 10W or 12USB power adapter when using one to charge.