Ever since I switched from using a desktop PC to a notebook for all of my daily computer tasks I never bothered to look back. It is just so convenient to always be able to carry all your work with you wherever you go. In reality I am not much of a road warrior though so most of the time the notebook sits on my desk for weeks on end attached to its docking station.
Obviously when plugged into the mains during the day the notebook's battery never gets used. However every time you turn the notebook off at the end of the day it will drain the battery ever so slightly overnight and will start to top it off again when it gets turned back on. The question is whether that will wear down the battery quicker than if you simply drain the battery and then reconnect the notebook to the mains adapter to recharge it a few times a day?
Over the past eight months I have done exactly that experiment, by using two identical notebooks. One has been connected to the mains adapter all the time, being used for approximately eight hours every day, the other has had its battery drained and recharged, usually once a day, but has also been running for eight hours every day. The results are somewhat surprising. The notebook that has been connected to the mains has a flat battery now, basically you get about ten maybe twenty minutes worth of power out of it before the notebook goes into standby. The notebook that has had its battery cycled does not offer the plus four hours of battery life it used to give, but is still good for more than three hours of use.
So although hardly conclusive it does provide some insights into why some notebook batteries go flat after not being used for months. The topping off that occurs after every power cycle when connected to the mains could very well be putting more wear on the battery than actually draining it fully and recharging it once or twice a day. Maybe notebook manufacturers should make mention of this? Or allow for the battery to drop to 80% of its capacity prior to topping it off again? The latter might reduce the total running time for the notebook on batteries by a mere few minutes, but could prove worthwhile for the longevity of the battery pack. Or, this could just be a 'feature' which ties in with the three months warranty that is usually applicable to notebook batteries which boosts the sales of overpriced replacements.