Well - I believe I have my Ergo Can Opener fixed!!! Thanks everyone for your help!
I replaced the batteries with a couple of 1700mAh NiMH cells. The originals had a couple of tabs for the wire connections. We were able to remove those and solder them to the new batteries.
While I had the can opener opened, I made note of which contact (in the handle) was +positive. The charging cradle that it sits in is "keyed" so you can only put it in one way. When I connected my new charger I made sure I got the polarity right. I left the diode in the can opener and closed it all back up.
The Adapter that I got is a Universal DC Adapter, 3 to 12VDC, 600mA. Not exactly what I wanted but it seems to work fine for some reason. It's a really super light weight adapter, not like those old heavy things they used to sell. I glued the polarity and voltage selector switches in place so no-one could accidentally change them.
I'm a little concerned about overcharging the batteries with an adapter rated at 600mA. I'm not exactly sure how that works. I've gotten some conflicting information on that issue. I think of current as something that the circuit draws. If it doesn't need it, it doesn't draw it.
I've been keeping an eye on this thing. Nothing seems to be getting hot. There may be something in the adapter circuit that prevents it from overcharging.
Any comments are appreciated!
Thanks again!