Im using a basic run of the mill battery in my Merc. It was in there,and had recently been replaced, when I bought the car. In the past I would leave it 'til it died on me then sort a new one ,but experience has taught me they can die at any time ,usually in the middle of nowhere ! I feel it has had a good caning what with running the compressors etc,so I think I'll replace it now.Without going into the realms of a second mortgage ,does anyone know what the good reliable makes are? or is it just a case of talking to my local factors? Does a higher capacity mean larger physical size (oo er!)? It has to fit in the normal battery position .Would the standard alternator cope with a higher AMPHR battery?