This comment made me think that disconnecting the battery was no point at all, because really - how would the computer be able to switch on by it self. So... I had my mac flipped around and was fiddling with the last part of the guide when I all of a sudden hear the start up sound! Don't know how and why it did. I turned it around with it guts open and guts hanging out. Screen was on. I forced it to shut down by keeping the power button down. Turned it back and first thing removed the battery cord.
Luckily the computer started up just like normal. But hearing that sound was just too scary.
BTW I had been cautious to de static myself multiple times.