WARNING: A couple of days after this project was completed, the Pleo died. I don't know if there is a connection.

The Pleo robot dinosaur takes insanely expensive $49 battery packs, which also didn't work well for us (or the charger didn't work well). But it's pretty easy to convert it to run on six ordinary NiMH AA batteries. The project is inspired by this one, but takes a somewhat different route.

You will need:

one 6 AA battery holder that can physically fit in the Pleo's battery bay (I bought one from Radio Shack)
a piece of string
a drill
soldering iron and lead-free solder
electrical tape

Step 1: Make Battery Holder Fit in Pleo

My battery holder fit very nicely into the Pleo's battery area. However, when I put six AA batteries into it, I ended up cracking the outer bezel of the battery area. To prevent that, you may need to sand, file or Dremel the holder to slightly smaller dimensions. Instructions online suggest that removing some of the plastic that's between the batteries will help.

Or you may be lucky and it will all work just fine.

Step 2: Add Loop

On the side opposite from the wires you will find two holes. Drilling a third hole from one side of the holder to the other lets you put a small string loop in that you can use to pull the holder of out Pleo. Tie a string loop. I ended up heat sealing the loop with a spoon heated over an alcohol flame, but if you're good with knots you won't need to do that.

Step 3: Cover Up Exposed Contacts

On the side of the battery holder with the two wires, there are a bunch of exposed contacts. Cover them up with electrical tape in such a way that the tape won't come off as the holder is pushed in and out.

Step 4: Solder Holder Into Position

This is the trickiest part of the project.

Remove any batteries from the holder.

Inside Pleo's battery area, there are three spring contacts. One is labeled + and another -. Solder the red wire from the battery holder to the + contact and the black wire to the - contact. Double check polarity. The + and - labels inside the compartment are hard to read. My photo may help.

Soldering here is tricky because it's hard to reach inside with a soldering iron. I ended up making and tinning little hooks on the ends of the wires, carefully hooking them on the contacts, closing the hooks with needlenose pliers, and then finally soldering into position with a soldering iron. Fortunately my iron (a temperature controlled one that my mom got me for Christmas) fit well into the cavity. I used lead-free solder since this is a toy after all.

And you're done. Make sure Pleo is off when you load batteries. The battery holder should fit snugly inside Pleo and can be removed by pulling on the string loop.

Now if I could figure out a way to make the toddler not be terrified of Pleo.