I'm not certain anyone will ever see this (so few submissions to the handheld reference section). When I got my virtual boy, it didn't have the battery cradle (which goes on the back of the controller). As a result I was unable to power it. I found that the VB accepts 9 volts, so naturally I grabbed a 9 volt battery connector, opened the controller (don't worry, it uses regular screws) and hooked it up to the battery terminals from the inside. Obviously I couldn't fit the battery in the controller, and I wanted the battery to be user replaceable, so I lined up a file where the controller wire comes out and filed the bottom of the controller just enough to fit the wires through as seen here: (looks better IRL). I soldered to the VB battery terminals (hard to do without melting the plastic) as seen here: (Mr. Blurrycam payed us a visit, but to clarify, what I did was push the battery connector leads up through the holes in the VB battery connector terminals, fold them over, and solder them in place.
Glad to finally contribute something to the community, normally I just ask an absurd amount of questions
Reuben

Sweet! How long does it last?

Thanks! I've used if for about 2 hours, so I'm not entirely sure. Although, if I were to guess, I would say in the vicinity of what the original AAs would last, seeing as AAs have around 1000mah and 9v is slightly less (but the 9v is probably more efficient because it isn't in series like the AAs would be to reach the necessary 9 volts).

Reuben