Power on 5V GPIO power pin at boot

Question

I am new to the Raspberry Pi, so I wanted to describe my project along side my question. I have a functioning Raspberry Pi A+ and I am building a heads-up display using a MyVu Crystal. This link gives a good idea of what is going on in my project:

Anyways, the pendant that controls the MyVu Crystal has a small lithium ion battery which is shot. Normally, this battery is charged via a mini USB plug and the device runs off the battery. With the battery shot it won't power up. In Martin's project above he removed the battery and connected the wires which originally went to the battery to the power and ground wires from a USB cable. It then ran directly off the USB cable via a powered USB hub.

In my project I would like to remove the battery and connect the board directly to the 5V gpio power pin and the ground pin. I am thinking just cut the wires to remove the battery and use two female-to-female jumper cables.

So here are my questions:

1) Does anyone think this won't work, given if you connect it to the power line of the USB cable (which supplies 5V)?

2) How can I set the Pi to supply power on the 5V gpio pin at boot to turn on the display?

There does not exist much documentation on the MyVu Crystal so I don't really have much information on the battery.

Answer 1

It should work.

All the Pi's gpios are 3V3.

The 5V pins on the expansion header are not gpios, they are pins connected to the 5V power rail. In effect they are directly connected to the microUSB power socket.