We offer 2 sizes of alternator 50amp & 95amp, as far as your choice of output is concerned, ideally you need to know the current drain of everything that you have fitted e.g some vehicles nowadays have electric power steering, even heated front and rear screens and a huge array of spotlights.
If you have spot lights, many modern LED spot lights have a relatively low current drain in comparison with older HID systems, the larger 95amp version will give you more capacity.
Remember the alternator can charge your battery quicker with a larger output, it just gives you that extra comfort and piece of mind.