Dose it affect the battery if a user kept it plugged in a laptop and never takes it out even though the battery has been fully charged, i mean dose it decrease the battery’s life this way?
The charging circuitry should be aware of the charge state and not try to overcharge the battery. One factor that could reduce battery life is the heat generated by most laptops though.
I don’t know how much they’ve improved, but as olyteddy was saying it will still decrease over time even if your not using it. Best thing to do would be remove the brand new battery and use a UPS just in case the power drops. If your mobile with it just leave it in, would be silly to pop the battery in and out.