Quoted from Nokoro:Honestly, that’s what scares me about changing the battery with the power off. It would be nice if someone could put together some step by step instructions. I would definitely do it to avoid the risk if I knew better how to deal with BIOS settings.
Basically you would remove the battery with game off, replace with new battery and close it all up, then plugin a USB keyboard via the usb cable in the coin-door and turn the game on, find and change the Multi-Monitor setting in the BIOS, save the settings and reboot.
If you need step-by-step on how to deal with the BIOS that could probably be done by someone kind enough to put together a few screenshots next time they do a battery swap.