I was watching movie and suddenly laptop went off. On connecting with charger I found battery is 76% charged and laptop could be turned on.
Once I removed charger it immediately went off again. Now, even though battery is in, it will not turn on if charger is not connected.
FInd out the setting in which your laptop wil shutoff on low battery. It is possible that is set for <75% (although highly unlikely). Check that first, then let us know what it is set at. It is in the control panel.