Aviod deep discharges (below 20 %) and avoid keeping a fully charged battery on charge at 100% capacity. Keep the temperatures of the system down as much as possible. No matter how well they're treated, you likely won't get more than 2-3 years out of a lithium battery and it's not a bad idea to replace them in this time frame, as it is common for the battery to swell when the end of its life is near. Variances between batteries are largely due to manufacturing in addition to duty cycle -- like anything manufactured, some last longer than others.  
Suppose one uses the laptop like a student does every day.  I am not asking best way to maximize a single run time on a fully charged battery, but my question is if my battery health is excellent or good now, what is best practice to prolong its life span before its health drops to “need to be replaced”. my intuition is not to let it drain to 1% unattended for long period of time.   whenever it drops below 20% or some level I should charge it back to 100%.  But somehow I also recall the battery has limited number of fully charged cycles which goes against frequent charge back to max. I do not know but I have seen same model brand new latitude laptop used by different users who supposedly use it for about same amount of years in same temperature environment, now one battery is swollen and not detected by bios, while the other still good.  How does charging habit affect life span?  What would be the worst practice I should avoid, if I do not know the answer to best practice?
What is best practice to prolong latitude battery lifespan