My y580 is brand new. I got it last Thursday and I stumbled upon an error. My battery is stuck at 55% and will not charge. If I plug it in, it says "plugged in battery not charging". Please help me ASAP.
You've probably got the 'battery health' option selected rather than 'battery life', under the Energy Management thing that Lenovo puts in your system tray. Mine just did this and I'd found this question but had to find the answer elsewhere, so I thought I'd pitch it in.
Try to remove your battery and attach only the AC adapter to the laptop and turn it on. Then attach the battery while the laptop is still on and see if it will start charging. If this doesn't work then contact customer support.
It's just a setting Power Options setting that prevents the battery from being charged beyond a certain point as stated by periphrastic.
The theory is that the closer to capacity the battery is charged to the higher the charge held by the battery. While fully charging the battery maxes out how long the laptop will run on the battery, it also degrades the battery. Therefore, the longer the battery is near it's maximum capacity, the shorter the battery life can become due to chemical reactions within the battery.
Many laptops only charge the battery to a pre-determined capacity and must be overridden by the user to charge to 100%. This allows you to keep the laptop plugged to the AC outlet for a long period of time without having to worry about overcharging the battery and cause it to die prematurely.