Battery for 1.6 with 2 year garauntee can be purchased for E60 for any car parts shop or abetter quality battey for about E85 - E90 with 3 year garauntee from somewhere like Halfords.
I just bought a car battery for an opel vectra 1.6, 1999. Cost me 67 Euros from the DIY store beside Tescos on Aughrim Street. I've disconnected the old battery and I'm now struggling to get it out.