The first thing is to find out what batteries are available to fit your car. Look for the size reference (normally a three-digit code eg 063). Other considerations include cranking amps (CA), which is the maximum current a battery and deliver in one go, and amp hours (AH), which is the total amount of electricity a battery can hold. High-end batteries are generally best suited for specialist applications so a decent mid-range one (such as Halfords) will be fine.