I have done some serious testing and have made the following discoveries:
The gamecube 3.4v line can accept a much higher voltage. I have put 3.4v to 5.0v through it and everything works fine. Amp draw is about the same on every voltage I've put through. 0.8A to be exact.
As explained before the 5v line is not needed. The memorycards only use the 3.4v line. I have however not tested a memorycard with a higher voltage. That will be tested soon.
The controller will also work with voltages from 3.4v to 5.0v. You can connect the 5v rumble line to the same controller voltage input. That way when you have a small 3v rumble motor you can have a decent rumble in game.
The wiikey which also uses the 3.4v line can also accept higher voltages. I have also put through 3.4v to 5.0v and it still works properly. This also means you can rewire the 5v line from the disc connector to the 3.3v line on the wiikey. Making it connect without extra wires to the discdrive port. If anybody could make a little pcb they could make things allot easier for people who can't solder that well.
Now the whole idea of all these tests are that you can run the gamecube with one 3.7v battery and one regulator. As the gamecubes 3.4v line can have higher voltages the battery can be connected directly. All that's needed is a regulator to output 1.9v which can handle a 6-7 amp draw. This one for example (PTH04T240F)
I also did some game testing and have found out the that you CAN play region games not of your region. I have connected a PAL gamecube to the wiikey switch in PAL mode with the dipswitches and was able to play allot of USA games. Some games just show up with a black screen after the gamecube logo boot but many games I've tried work. The video output isn't always that good because of the way the PAL gamecube video chip handels the resolution. Some games won't fill the whole screen but hey it's better than not beeing able to play out of region games at all. This will also work on USA games with PAL games as far as I know. That has not been tested though so let's keep it open for now.
