Here is what i know about lithiums. Maybe someone can correct me where it's wrong
--you can charge them as and when required.
This means that you can plug in your charger when they reach (say) 79% and take off the charger when they reach (say) 91%. This type of charging doesn't affect them in any way whatsoever, unlike older batteries, because there is no memory. It doesn't matter when you plug in the charger and it doesn't matter when you take out the charger. You don't have to unplug at 100%, and it makes no difference.
To maximise the life of a lithium, as a general rule, plug the charger in anytime after around 30%. Deep dischages (ie discharging down to around 0% to 5%) regularly can put a strain on the battery and shorten their life.
--lithium is highly volatile. For this reason they have lots of inbuilt safety mechanisms. One of the mechanisms is to prevent them from either over charging or from fully discharging.
For overcharging, the charger will switch off the current at 100% (if you leave it plugged in overnight it will drain to about 90% or so and the then start charging back up to 100% again, and this cycle will continue until you unplug it. You will be able to see this behaviour on a graph when you use an app such as Android Tuner)
For discharging, it's recommended that they are not drained to 0%. Although it says "0%" it's actually not 0% because that would cause some serious damage.
--the most ideal charge cycle for lithiums is to charge from (very approx) 40% to 80%
--Some sources say that it's useful to deep discharge them down to "0%" not more than once per 60 charge cycles(plugging in at 50% and then discharging them back down to 50% is half a charge cycle). Otherwise, avoid discharging it down so low
--heat is the worst thing for lithium batteries. Hypothetically, if you (say) browse the web for 5 hours when you're in the hot midday sun(NB this of course assumes you live somewhere other than the UK where it's permanently cold, wet, and miserable), then your battery will dischartge more quickly than if you did exactly the same at cool room temperature