Motherboard light remains on after full shutdown including forced shutdown by power button. How do I stop this..?

The motherboard light staying on after shut down is normal.

If the PC doesn't shut off after you give the shut down command, hold the power button a few second and it will turn off.

If a p.c is shut down as you say but the Power supply is still connected to the mains supply the power supply will still supply a +5V to a section of the motherboard. This is there mainly to detect when the power button is pressed and will cause the motherboard to give a Start signal to the Power Supply.

Disconnect the power supply from the mains supply and that LED will go out

take out the battery?

UNPLUG IT WHEN YOUR DONE