If it's anything like all the other screens out there, you have wired it up incorrectly. Looks like you have connected two video signals at the same time. This guide shows you how to wire it up correctly:

http://www.sudomod.com/forum/viewtopic.php?f=22&t=958

Yes, I have it like that at the moment, but I wanted the leds on when the pi was on. In the middle of intense gaming I'd probably forget to check the battery status.

I don't think the leds on the board show a low power status. Two are for charging status (red for charging and green for fully charged), and the other blue one is for power. I think the holes on the board for leds are there in case you just want to extend the existing leds instead of having to desol...

I think you leave the battery connected permanently. You wont be able to put a switch between the battery and the PCB without repriming it. That's annoying, but thanks for the info. I was trying to hook up a low power led board the other day via this power board and I couldn't get it to work, but n...

Maybe these 1.6mm high switches would help?
https://www.sparkfun.com/products/8720

What is trying to draw so much power? It sounds like you have something plugged in that is eating up the current. You will either have to find the device that is wasting all that power or get a different power source that is capable of discharging at a higher rate to power it sufficiently. From what...

I think you will always have the rainbow box unless you're using close to a 2.5amp power supply. The official power supply for a pi3 is rated at 2.5amp and the powerboost is 1.8amp max I think. If everything is working fine, a rainbow coloured box on boot up isn't a big problem, looks pretty.

In Wermy's guide here:
http://sudomod.com/game-boy-zero-guide-part-4/

If you scroll down you will see a photo of the speaker, and he shows that holding it in that orientation, the right terminal is positive.

@damian If it's a v7 bw board, in the wiki it says that it doesn't require any mod to run off 5v, so why have you soldered the yellow wire on? http://sudomod.com/wiki/index.php?title=BW_3.5_Composite_Display Also your video signal may be on the other channel. Perhaps it's just one of a combination o...

Don't know what encrytion type your router uses but there's a guide here showing how to set it up:

https://github.com/retropie/retropie-setup/wiki/Wifi