Posted July 18, 2013
Sactravas: Somethings to also remember is even though batteries don't have memory effects anymore, having a battery and power cable plugged into a laptop for extended periods of time will put a wear and tear effect on the battery, meaning when the battery is fully charged it will drain itself to protect itself from overcharging; it will continue that cycle over and over again. Protect your batteries and don't have it in your laptop unless you're on the go, go.
I've never heard this claim before so I went and checked it out and this doesn't seem to be true. Laptop batteries are damaged by 2 things: the drain/recharge cycle and heat - as they cause the internal structure to warp/break down.
So leaving the battery in while on mains power doesn't damage it because of being topped up (I've actually read somewhere that you aren't supposed to let Lithium battaries drain below 50% or something anyway..), it is being damaged by the heat generated by the device. Usually, if you have it plugged in, it is on for longer and thus, hotter for longer.
Bear in mind this was just a quick 10 minutes of Googling, but it makes sense based on my other knowledge of how these batteries work. Please point me to a correction if it is wrong! :)