I just wish someone would answer the man with a legit answer so we can know for sure.
ashimoke replied with a link from nitro2k01 with tests and results of a gameboy running at 9v.
I tried feeding my known good Gameboy with 9V for a few minutes, with a moderate contrast setting, without any problems. However, it’s possible that the extreme positions of the contrast dial will slowly destroy the LCD, when the input voltage is >7 V. If so, it could probably be fixed by changing the control voltage range for the contrast dial.
I’ll have to investigate that further, but my preliminary conclusion is that you can feed the Gameboy with a 9V battery without problems.
what i think we could do is simply get a 9v battery and get a regulator in there. solved.