Humm. Now I'm not sure if it is do-able... But if you want to try, and possibly risk the pet... I've got an idea. Get a copper thin. really thin, peice of copper. Cut it To size. Carefully try to add a tab either on the metal itself. (Cutting a tab piece) or add a carefully placed piece of stronger Paper into a tab like ... well. a tab. So you can remove it if it doesn't work. Carefully try to cut it as small as you can but not too small, Trace a battery (cut on the line and possibly make it a tiny bit smaller... ) Do the tab thing, make sure... Then place it into the side that is peeling. Hope it works once you put the batteries inside.
ALSO, keep in mind, sometimes batteries in other virtual pets go in dfferently then a tamagotchi...
So... In a slightly less confusing list....
Thinner small piece of Copper metal. Not wire, just a small sheet.
Trace a LR44 battery on the metal copper piece.
Decide if you want part of the metal piece you trace a small tab in metal or paper.
Cut the trace out, with or without a metal tab. (The metal piece that you leave for the tab doesn't need to be thick, just tall enough you can grab it out if it doesn't work....I'm having a slight issue explaining this)
If you didn't add the Metal tab to the traced, cut out a piece of paper... Carefully attach it to the traced piece.
Make sure the tab is fully attached and wont fall off if pulled.
Place it in very carefully.
Batteries. This is the test. Be careful not to touch the copper piece as it will conduct the power from the battery and the inside of the virtual pet.
Other notes.... If you choose to do this... Be careful when removing the batteries. They can become warm/hot....Make sure not to touch the tab at all until you are sure the virtual pet is cooled off. It is possible this can explode the batteries inside... So please think about what I am suggesting before you do so. I can't be held responcible if you chose to do this, I only supplied an idea that may or may NOT work. I bid you the best of luck if you do try this.