Go to the Kwik Fit website and locate the "Batteries" tab, enter your registration number and post code, then press search. The website does all the work for you and then you can do a search for the best price for the battery you select - do not have to purchase from Kwik Fit.
Note that the most important attribute to your selected replacement should be dimensions. It MUST fit into the battery tray and be held securely in place, it would be an MoT failure if not secured.
N6 JMX