We alwayw fit genuine batteries. They Last longer, they seem to eliminate some electrical gremlins and they fit well.
I replace them often and some have been 10+ years old. On a CL the other day one was 15 years old!!
Long life servicing is not good in our experience. There is a VAG specilaist near us that sees regular engine failure and serious wear on cams etc and he put it down to th elong service intervals. For the small cost an oil and filter is going to be, i'd just do it.