In addition to what has been said already. As you're using Linux you might be able to use magic sysrrq to enforce a reboot on kernel level. I've had similar issues with broken disk arrays which prevented proper shutdown and reboot. So you might at least not have to wait until your battery drains completely.
Assuming 'magic sysrq' is enabled in your kernel (kernel config
CONFIG_MAGIC_SYSRQ) you can use Alt+SysRq+b to reboot the machine.
NOTE: This is forcing an immediate reboot without unmounting any HDD cleanly. So a file system check on next reboot might be required/recommended.
If you're running a graphical user interface like KDE or Gnome, then either switch to a console (using CTRL+Alt+F1) or try CTRL+Alt+SysRq+b from the GUI.
You might also have to check whether your kernel has magic sysrq enabled by typing
You can also initiate a sysrq-reboot on remote systems:
echo 1 > /proc/sys/kernel/sysrq
echo b > /proc/sysrq-trigger
This would lead to an immediate reboot if
CONFIG_MAGIC_SYSRQ was compiled into the kernel.
More details on magic sqsrq can be found here.
NOTE: on the Samsung Series 9, the key labeled "Fn Lock" serves as SysRq, though it is not printed as such.