I heard that charging a Li-Ion battery all the time is practically harmful for the battery and significantly reduces its useful capacity over time. Is this true? Should I disconnect the power cord from my laptop every time it isn't used for a long period of time, for example, at night?
If the answer is yes, does it apply to only bigger batteries or to smaller ones (for example, cellphone, tablet) too?
Li-ion batteries tend to deteriorate faster if left 100% charged (and of course may be ruined by complete discharging). "Overcharge up to 5.2 volts leads to the synthesis of cobalt(IV) oxide... The cobalt electrode reaction is only reversible for x < 0.5, limiting the depth of discharge allowable." Also, when left fully charged, the lithium ions, intercalated in the negative electrode, cause it that electrode to slowly expand and lose cohesion. For that reason, laptop manufacturers such as Toshiba, Samsung and Sony have added a power mode that limits battery charge to 50% or 80%, if the laptop is used primarily from the AC mains.
For that reason, you might intentionally discharge the battery halfway and remove it, to extend its life, but the disadvantage is that it no longer functions as a UPS. A better option would be to find a utility similar to the Samsung Battery Life Extender that would keep the battery at ~50-80% charge.
