If you're going to collect these things, you're going to need a few tools and extra batteries.

This is from my failed attempt to get my newly bought Pocket Biscuit going.  :0Just every once in a while, newly bought pets can be dead, never to be revived again.  :0(

The batteries had gone terribly bad and eroded the battery contacts in the circuit board.
So, any way, you're going to need at least the average small screwdriver kit. When in doubt, go for the flat head, not the Philips.
The sizes start at .09mm and go to 3mm.   The most used are the two smallest sizes.
It seems that I am constantly using them.

When they are not working, it's usually a matter of cleaning out a little dirt inside or doing a little soldiering in there if there is a disconnected wire.  But then again you might just want to yank out that wire if your pet is just too loud and there is no sound off option!
But some times there's just nothing that can be done. :0(
I have four dead pets in my collection.
Stuff you're gonna need!
The batteries you usually need for these are:
Different names, SAME SIZE!
There's a larger flatter battery for some pets, (pedometer pets and a few others) That is the CR2032 but most take those average button cells.
The handy dandy volt meter.
Just in case you have a little battery mix-up you can easily tell which ones are good.
The botton cell batteries are 1.5 volts.
The larger flat ones are 3 volts.