Is the chip the right way round? Do you have the pins wired up in the correct order? (Sorry if this sounds annoying but it's always best to ask to ensure that it's not the issue)
The voltage of the backup battery should not affect it. I would suggest connecting the battery connection to ground to ensure it's not a funny battery though.
If you have a multimeter then check the voltage between 5v and gnd (on the chip) to maks sure that power is getting to the chip.