Occasionally I forget to turn off my Nikon SLR. This is especially true when I have connected it to download some pictures. The USB connection keeps the screen alive and the EN-EL9 battery pack is dead in less than hour. Usually it will recharge. But sometimes it will not stimulate the charger and will not charge, no blinky lights, nothing.
As I understand it, Lithium Ion (Li-ion) batteries have a circuit inside that limits the charge current and keeps them from overheating during charging. When the battery is completely dead, this circuit has no power and it cannot allow current in to charge the battery.
I have been able to get around this by putting the battery in the charger, unplugging the charger, wait a 10-count and then plug it back in. Repeat until it appears the charge cycle is working (flashing light on my Nikon MH-23 charger). Monitor the charger for a few minutes. If the light comes on solid too soon, slip the battery out of the charger and back in. Check for normal charging activity. I hope this saves you from buying a new battery.
Hold fast, run free – the blatherings of CBCalvin