Good luck man. I've been there and it's scary as hell so I know.
I will say this, you shouldn't need to wait for the battery to run out to reboot. If you're trying to get to the bootloader and you have a black screen, you can try this.
Normally, doing a Press/hold the power button and press/hold the volume up button for about 10 seconds will simply reboot the phone. However, if you're trying to reboot to the bootloader, you can try this.
On the 10th second of holding the power and volume up, without releasing the power button, quickly release the volume up and press/hold the volume down button. It might take a few attempts but if it works, it will get you to the bootloader. I've tried it on mine a few times and it worked for me.