I would clean it, check the water add if needed, slap a slow charge on it, and start up your mower every month or so. I do this with my equip plus my bass boats, and the batteries keep their average life exp.
Actually, the storing of a battery on concrete is an old myth. This subject was brought up sometime over the summer, and someone gave us the site of a battery company that had care tips and such on it. Interestingly, that was one of the things they said and backed it up with facts to prove it. I always believed this too.