I just got a Halfords battery for mine, seemed to do the job. Fitting is dead easy too, just get the service manual downloaded and you'll be fine. You have to remove quite a bit of plastic trim around the battery and bottom of the window, but it all slots back together easy enough, just take your time - especially as its cold and the plastic will be brittle.
I think I will go and remove the neg connector and just leave it till it warms up and/or I need to use it