You are basically asking if you need to calibrate the battery and I've heard answers on both side about that so I agree go with what the maker says.
What kind of laptop is it? Dell has a special feature called Desktop-mode battery charge. What it does is if your laptop is plugged in for some many hours it will automatically adjust the charge levels of the battery. The adjustments include regularly allowing the battery to discharge, even while plugged in. The benefits help slow the reduction of charge capacity over time and may even decrease the need to purchase a replacement battery during the life of your laptop.
I have an Alienware and awhile back i noticed my i was plugged in and the battery was discharging while plugged in and...