I am looking to replace the battery in my car, however I am having some confusion about the correct one to buy.

On the Halfords website it recommend that I need a '075' battery

On the Europart Website it recommends a '027' battery

Does anyone know the difference, does it matter which of these I buy? I have no idea what these codes mean, but obviously don't want to spend money on a battery that won't fit/work in my car!

To confuse things I had a look at my current battery and it just says it is an s50 with 390mha and 65ma (or something like that - i forget the units)

I just want a cheap battery which will allow my car to start in the Winter - my current doesn't (but then again it is at least 7 years old)!

thanks