I don't read that article the same way. I suppose if you're only running the Mini from AC and never from battery, you could remove the battery but this seems to me to contradict the whole point of a netbook. The article refers to batteries getting hot in notebooks, but the design of the Mini does not lead to that. The charging circuit shuts off when the battery is full.
If you have a spare battery, then sure, leave it at 40% charge in a cool place. But a ritual of removing the active battery from the Mini seems misguided to me.