In terms of a power slot, do you mean a 9v adapter jack, so you can plug it into the wall? That wouldn't be too hard of a mod. Is that what you want to do?
Yeh, 9v adapter jack so I can power it using the usual wall power adapter unit.
Well, get a 2.1mm 9v switched jack, and take the red wire from your battery and wire it to the switched terminal, then wire the "hot" wire to wherever the battery wire used to go, and then make a new wire from where the black wire of the battery goes and put it on the "cold" lug of the jack.