Originally Posted by exdeath
You are better off drilling a hole in the plastic and soldering in a barrel connector in parallel with the battery terminals for an off the shelf 6 volt DC power supply (dont use it with batteries at the same time lulz).
that's what i'd do pretty much.
you got a multimeter right? it helps to have around and you can get one from harbor freight for ~$3
go to goodwill and pick up a 6VDC power supply for $1 from one of their boxes of junk power supplies
you could either solder the power supply directly to the battery terminals + to + and - to -, or solder short lengths of wire and use wire nuts if you want it to be removable. i doubt you'd have space for spade connectors & batteries at the same time.
drill a small hole for the wires or find a space where they'd fit through ( like by the opening tab ).