Is it better to keep a laptop or smartphone battery always at 100% or to let it discharging before recharging? [duplicate]

10 years ago when I was doing hardware support it was best practice to fully drain a laptop battery prior to recharging in order to maximize its life. Is this still the case or can a battery now be recharged at any point without worrying about shortening the lifespan?

NiCd and Nickel Hydride batteries need occasional deep discharging. Lithium batteries do not suffer from the same issue - and deep discharging can damage them. This article discusses the subject in more depth.

For lithium-ion, it is actually now considered bad practice to completely drain the battery before recharging. NiCd and NiMH batteries need this to be done to minimize their so called "memory effect" - not so for Lithium Ion. In fact, it will actually be harmful for Li-Ion batteries.

I quote you this paragraph from this link

A lithium-ion battery provides 300-500 discharge/charge cycles. 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.

There are many other sources online that support this statement, but I know this from my long-time exposure to battery conditioning due to certain hobbies (e.g flashlights).

From Wikipedia's entry of Lithium Ion batteries :

Lithium-ion batteries should never be depleted below their minimum voltage (2.4 to 2.8 V/cell, depending on chemistry). If a lithium-ion battery is stored with too low a charge, there is a risk that the charge will drop below the low-voltage threshold, resulting in an unrecoverable dead battery.

Lithium ions seem to have different issues, more to do with how far you drain them and how you store them http://en.wikipedia.org/wiki/Liion#Guidelines_for_prolonging_lithium-ion_battery_life

I believe there's not really "battery memory" anymore with modern batteries, but it's a good idea to run down completely one time from a full charge to calibrate the "remaining time" left on most laptops. I've done this on both Mac and Windows laptops and it helps.

Nope, although every 10-20 charges, it is best to in order to calibrate your battery (otherwise you may see it saying 2 hours left and then going flat after 20 minutes!)

You are referring to the "memory effect". Typically, Lithium Ion batteries (most modern gadgets use these) do not get affected by this.