Battery help, can I use 1 power port to do everything?

[WhiteAndBrown]

Okay so i was looking a shock slayers plug and play diagram for batteries in a portable and i want to do the same but only use one power port.
I could have one power port that goes to a on off switch that powers the GameCube and charges the battery at the same time when ever that plug is powered.

Now i was wondering how I would wire up the batteries to power the GameCube with just one switch. Instead of taking the batteries power and wiring them up to another on off switch to turn on the batteries. I want a switch that can put these together.

I'm pretty sure there is a switch that can do what I;m looking for but i don't know what switch that is or how to wire it up.

For example, with 1 power port and 1 switch
1st position is off, nothing is connected.
2nd position uses 12v wall power to power everything and charges the 12v battery pack at the same time.
3rd position uses 12v battery pack to power everything. Wall power is disconnected.

Any help would be very appreciated.

Battery pack I'm using - http://www.ebay.co.uk/itm/261397183356? ... EBIDX%3AIT

 

[Bakuku]

viewtopic.php?f=45&t=53

Hopes this helps you.

 

[WhiteAndBrown]

Thanks it will help.

Edit:
Ashen says if you can fit two ports then he highly recommends it. maybe i should and not risk damaging my portable.

Oh well i can live with it

Thanks for the quick reply though