According to the spec attached it is 80Ahr. But I doubt the existing one is that big but I can't see the label of the battery to verify. Size about 280mm(L) x 170mm (W) x 180mm (H). Please get the closest Ahr for this size.
I discovered that the battery isolator really very handy. Previously my elise light weight battery would not last for 2 weeks even with the alarm off. Now it will start right away after 3 weeks.