Something I would like to find: A regulated nine volt power supply that has an adapter that fits in the battery compartment and provides exactly the same power as a nine volt lithium battery without enriching the energizer bunny folks. Is there such a thing?
I can make the battery compartment insert if I can get the right power on a pair of wires or terminals, but I'd rather find the package if it exists.
(Yes, I know about recharging, and yes, I forget to do it.)
You can buy battery snaps that connect to a standard 9V battery terminal. By connecting this to a regulated 9V AC adapter, you have your result.
The regulated wall-adapter is easy. Here is the first one I found with google:
Or, you could simply build one yourself using a non-regulated 12V adapter.
You will need to build the interface between them, such as it is.
I have a logitech wireless keyboard that eats batteries like popcorn. It doesn't work on rechargeable AA batteries, probably due to some voltage requirement (primary cells are >1.5V when new, whereas secondary cells are nominal 1.2V). So, I bought a surplus 8.4V liion battery, built a little regulator circuit, and two cells + the regulator fit into a cute little box hanging off the keyboard. However, even with this, it still sucked (just not batteries) so I gave up using it. It would lose synchronization with the mothership, and you had to take the batteries out, hold down the keys for 30 seconds, put the batteries back in, hold the button on the mothership pod for 15 seconds, and push the button on the back of the keyboard (as documented on the logitech site... sigh). This would happen once a day. My belief was that the microcontroller running the keyboard was locking up. Junk.
These are designed to snap onto a battery, and provide power to the circuit. If you're going to connect one of these to a power supply, be sure and reverse the red and black leads, because they'll be wrong. In other words, the negative of the supply should go to the red lead of the battery snap, because that snap will snap into the one with the black lead on the equipment side.