This time, I found some more suitable parts. First of all, you need to make sure the pin layout are correct:-
The USB sockets for those computer back panel is superb for this purpose. Better than last time the USB->PS/2 adapters.
So, I go and buy a small plastic box, it costs only two dollars. And to host the batteries, a $5 box is used. I'm talking about HKD.
Since this USB back panel socket has threaded screw holes there, attaching them to the box is so easy and elegant:-
To avoid the battery container from moving around inside the box, you can add some foam inside to eat up the empty spaces.