sudomod

Hello Friends! I have a very basic project coming up, and I want to make sure I'm safe with it. I have a 1200 mah 3.7 volt battery laying around and I want to put it in into a basic nintendo flavored gameboy advance.

https://www.youtube.com/watch?v=xUQKAWbxvlE

I found this video on the subject but his work seems very shoddy and idk whether to trust him too much on it. ( sorry if you frequent this forum don't hate me T_T ) Is it as simple as this guy makes it seem?