I do not leave the laptop plugged in when the battery reaches 100% because I have noticed a screen flicker (as discussed in another thread). I recently started running an external monitor via HDMI. The external monitor does not flicker, but the laptop monitor still flickers with a full charge, so I tend to unplug it, let it run awhile and then plug it back in again when I notice the battery is getting low.
Unfortunately, today the laptop suddenly died again while running the external monitor. The battery indicated 12% charge as soon as I rebooted.