Li-ion batteries don't like to be charged to 100%, nor discharged to 0%. Doing so slowly reduces the maximum amount of charge they can hold. The structure inside the battery which holds the electrical charge actually grows and swells as you charge it. Charging it to 100% puts more physical strain on the material, causing it to fail more quickly. The batteries used in electric vehicles are commonly only used between 20%-80% charge for this reason.
https
/www.popsci.com/science/article/2010-12/lithium-ion-batteries-swell-and-contort-while-charging-new-study-shows
If you want to keep your laptop plugged into AC power, you need to make sure it's not constantly topping off the battery to keep it at 100%. Li-ion batteries will slowly discharge with time, and an unregulated charger will immediately top it back to 100% when this happens. All these short charge cycles will kill your battery, and in a couple years you'll have one of those batteries which only lasts 5-10 minutes.
So when the laptop is plugged in and the battery is at 100%, you need to monitor the battery charge level. The most common strategy employed by laptops is to not top off the battery until it falls to about 95% or 90%. If your laptop has been constantly plugged in, and the battery used to be at 100%, but now you see it's at 98% or some charge level less than 100%, then your laptop is probably using this strategy. If you monitor it closely, you can see how low it goes before it tops off the battery to 100%. Usually it's 95%, but I've seen a few which go as low as 90%. The charge level before top-off isn't really what's important. The amount of time before it tops off the battery again is. Ideally you want it to top off the battery once every few days.
The other common strategy is simply not to charge the battery to 100%. Most laptops have a utility program which controls this. You simply set the max charge state at something like 80% or 90%. The battery will stop charging when it reaches that point, thus avoiding the harmful 100% charge level. (The function has to be built into the BIOS for it to work even when the laptop is off, so you can't add a program to do this.)
A few laptops deliberately mis-report their battery capacity to Windows. So it'll have a 54 Wh battery, but it reports itself to Windows as a 48 Wh battery. And when Windows says the battery is 100% charged at 48 Wh, it's actually only 89% charged (even though Windows reports it as 100% charged). These are a little harder to detect, though programs like HWInfo which report actual and current battery capacity may give you a hint.
Regardless of all of the above, you should charge the laptop to 100% and discharge it to 0% (or as close as you can) about once a month. This will allow the laptop to calibrate the battery. There's no magical way for the laptop to know exactly how much charge is in the battery. It guesses the charge level based on the battery's voltage. Since the battery voltage profile changes as the battery ages, if you don't calibrate the battery, eventually the % charge you see becomes meaningless. A full charge to 100% and a full discharge helps the laptop recalibrate, and make sure the % charge it's reporting is accurate. Yes it damages the battery slightly, but it's preferable to not knowing if you're possibly damaging the battery.
Unfortunately, the chemistry of each battery and idiosyncrasies of the charging circuit are unique to each laptop. For further guidance, you may want to ask other owners on the notebookreview forums, in their Asus sub-forum. They may be able to provide you with tips specific to your model laptop. As well as instructions on replacing the battery if it should ever need replacing.
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/forum.notebookreview.com/forums/asus.19/
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