I always keep my charger plugged-in and my battery remains fully charged. but sometimes when I restart my laptop it starts charging again and shows the battery is in it's 90's%. My question is should I leave the charger plugged-in so that it reaches 100% again or I plug-out the charger and use the battery to some level and then plug-in the charger?
In simple words, At which level should I recharge my laptop battery? Is it ok to plug-in the charger at 90% charge remaining?
I've found good documentation on Battery University: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
The most useful parts for you being, probably, the following:
The worst situation is keeping a fully charged battery at elevated temperatures. Battery packs do not die suddenly, but the runtime gradually shortens as the capacity fades.
and
The question is asked, “Should I disconnect my laptop from the power grid when not in use?” Under normal circumstances this should not be necessary because charging stops when the Li-ion battery is full. A topping charge is only applied when the battery voltage drops to a certain level. Most users do not remove the AC power, and this practice is safe.
Modern laptops run cooler than older models and reported fires are fewer. Always keep the airflow unobstructed when running electric devices with air-cooling on a bed or pillow. A cool laptop extends battery life and safeguards the internal components. Energy Cells, which most consumer products have, should be charged at 1C or less. Avoid so-called ultra-fast chargers that claim to fully charge Li-ion in less than one hour.
