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.
"When possible avoid frequent full discharges. Instead, charge the battery more often. There is no concern of battery's memory when applying unscheduled charges. A high residual charge before recharge is a benefit rather than a disadvantage for chemistry of Li-Pol battery on all iPads. The best way is to keep battery between 40% and 80% charged. **After LiP battery of iPad is charged to 80% capacity it switches to trickle charging with a potential to cause plating of metallic lithium, a condition that renders the cells unstable. One more incentive to keep battery of iPad between 40-80% is the rate of the charge loss when gadget is not in use. The charge loss amounts up to 6% per year when battery is fully charged, but only 2% per year when it is half-charged.** Nevertheless, short discharges with following recharges do not secure the regularly calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate full discharge and recharge every 30-40 charges fixes this problem." <http://thehowto.wikidot.com/prolong-battery-lifespan-for-ipad>