Basically the 3v models take a really odd looking battery with snaps (what you have on typical 9v batteries).
Expect to pay $9 plus shipping if you find one. And its still going to be alkaline; less life than a lithium.
The battery compartment for these cameras is on the left side of the back. A little notch lets you know where to open from.
More than likely the battery is dead, corroded, and probably both.
Remove the battery and cut the snaps off. Clean the compartment with some alcohol and swabs.
There are 3 screws, one of which holds the metal snap for the door.
To remove this piece you need to extend the bellows and move the focusing tab out of the way.
You can then remove the piece, taking note of the route the wire takes through the bottom.
To make sure your camera will even function with a new battery, get yourself a 3v source. Be it a 2xAAA holder or a 3v lithium holder. Connect the wires to it temporarily. Cock the shutter. With something covering the electric eye, push the shutter button and hold it. You should hear a single click. Wait a second or two, and remove your finger from the eye. If you hear a second click soon after, the camera is working. If you only hear 2 very fast clicks no matter what you do, the power is not reaching the circuits.
One click is the shutter opening, the second is it closing. Test different lighting situations and listen for the differences in timing. Bright light should make the clicks closer together than a dark place.
To get any new sort of battery holder to fit inside the compartment, some of the original holder needs to be removed.
A little elbow grease on some pliers makes quick work of it. You can file it down, paint it, whatever you want. I keep it rough since you only look in the battery compartment once in a blue moon
The plastic inside the compartment is very brittle, a little tweak with some pliers will remove these two tabs of plastic.
Of course try not to break anything but the red area. You’ll find it has its own fault line.
While I chose to mod this one to 3v photo lithium (CR123-size) batteries, you can also choose to use 2xAAA batteries. The choice is between the higher price of lithiums but the much shorter life of alkalines.
If you will use 2xAAA, simply connect the wires and that’s all. A typical holder will fit just fine with all the extra plastic you removed gone.
You’ll find these batteries in any store that sells batteries. The holder would be a little more difficult, Google can be your friend for those. Both can be had for under $9 total and will dramatically increase the time between battery changes.
Strip the 2 wires from the camera. I found using an xacto knife and shaving the covering to be best, the wires are flimsy. Using a soldering iron, tin the tips with some solder and flux. Do the same to the 2 terminals of the battery holder.
Just for cleanliness sake, use some hot glue to seal the connections.