They're a 3V rechargeable battery, apparently often used on motherboards. I need one for my Logitech K750 solar powered keyboard as after 18 months it's no longer holding much of a charge.
I see that Element 14 have them, http://nz.element14.com/maxell/ml-2032-t17/button-cell-r-c-pcb-2032-3v/dp/3031998, but they want $23.68 and it will ship from their UK warehouse. I found a few places on Amazon selling it for US$4 - US$6 but they don't ship to NZ. Jaycar apparently don't have them.