I got the Pox for Christmas. Not a lesser Pox, the Great pox, better know as Syphilis.
At first I thought it was a shower tool, to clean my... uh, parts.
And a No-Pen, retractable ballpoint with a button on the back.
If someone tries to borrow it, just point and push. It will hurl 14 different voices/variations of "no".
I looked up the batteries for the pen and found LR-44(A-76) range from 19 cents to $3 each, online.
But the Lava Egg takes no batteries.