Finally had a few minutes to do something about this issue and finally made a decision on the direction I wanted to go. I toiled with plugging into a wall, using re-chargeable batteries and having to take them in and out for charging, using one of my airsoft batteries, etc. I finally decided on just plugging it into the wall, since the garbage can sits right in front of a plug which is otherwise unused. Once I made that decision, I went back and forth on how I wanted to get power from the wall to the motor. Here's what I decided on:
First was to use my multimeter to determine how many amps the motor used in normal operation and when under extreme load (like forcing the lid closed while it's trying to open). The amperage was something like less than 200 milliamps (I forget now).
I started with finding something with open leads and a nice female plug on the other end. Found this:
DC Jack Adapter
Connected the leads to the battery springs:
Allowed a little slack for the plug:
Found a plug that fits into the female end of the other one:
DC power to USB
And then I plugged all that into this neat little gizmo that I have a thousand of, a good 'ol standard USB adapter for a cell phone:
It was just that easy! Now, all I have to do is drill a little hole and epoxy the female plug in to clean it up a little. For now, I just have the wire sticking out a little bit.
For day to day use, I just flip the switch and may or may not unplug it, remove the lid and empty my trash. I don't have to deal with batteries, charging, or anything else.