Simple solution is removed the battery, a better fix would be to Simply replace the battery. I don't have much experience with this series but it sounds like your battery overheat it and was shut down to prevent fire. This was a common problem with older series and the best solution was to set your charge thresholds in Lenovo Power Manager to prevent the battery from charging to 100%. I have batteries from 2007 that still work great because I don't constantly top them off. Mine usually start charging at 70% and stop at 90%. You can get very long battery life this way if you don't need to run off of battery often. In your case it sounds like you do not even need to use the battery but it's always best to have one it can't prevent a low voltage condition so it works like a power backup UPS as well as keeping your system from crashing should the power failure.
Credit: TuuS