Question: Should you discharge a Li-ion battery all the way before plugging it in?

Is it especially pertinent when you get a new battery / laptop?

Should you keep draining it all the time, or leave it plugged in whenever you can?

All battery tips are welcome.

Answer: 
Li-Ion degrades with use, so you should prefer shallow discharges. I.e., always charge it as soon as possible. This is in contrast to Ni-Cd and Ni-Mh accumulators, which *do* like to be fully discharged from time to time to keep their full performance.

So normally you should plug in your laptop whenever possible.

Another thing that is bad for Li-Ion is heat, which unfortunately laptops produce. So ideally, you'd remove the accumulator if you don't need it, and store it half-charged in a cool place. But many laptops don't work well/at all w/o their accumulator, so that's more theory.

See e.g.
<http://www.batteryuniversity.com/parttwo-34.htm>

> 
> The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.
> 
> 
> 

Or Wikipedia:
<http://en.wikipedia.org/wiki/Lithium-ion_battery#Guidelines_for_prolonging_Li-ion_battery_life>

> 
> Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled").
> 
> 
> 

You may need to discharge it fully occasionally to recalibrate the capacitiy measuring electronics in the accumulator. Every 30 cycles or so should be enough.
You should fully charge/ discharge your battery the first 3 times of use.
Then, vary the charge cycles. So, charge it to 90% then let it drain to 15%;
charge it 75% and then discharge to 20%.
This has been proven by myself, and a lot of people I've suggested this to (including a school environment of over 400 laptops) work well.

Then discharge fully / charge fully only once every 20 cycles or so.
And never leave it charging overnight - because this will cause 'overcharge' and eventually could fry the battery cells.

Good luck :)