Kind of a hard thing to have batteries inside an animal.
The microchips used for ID, don`t have any power in them, thus they can`t send a signal. The magic wand used to ID an animal sends out a radio signal, which is picked up by the ID chip, converted to power, so that it can send out the return signal.
RFID is a similar process, designed for goods, and used like a bar code. Again, it requires a radio signal to power it.