Batman is certainly up there in intellegence, but science wise, he gets out invented by Marvel big names like Reed Richards and Tony Stark quite often.
However, that may not be revelant. In comics, (and the real world for that matter) using your brains is not all about the science. It's often more about asking the right questions and finding the right answers. As an inventigator, he beats the likes of Tony Stark, and probably comes in somewhat equililant to Reed Richards. It would be hard to say they are equals, because as investigators, they tend to work in different areas. Bruce mostly investigates people (as a detective should) while Reed primarlily investigates the universe (like a scientist).
So to parapharase another comic character, Batman is the best (and smartest) there is at what he does. As long as what he does is being a detective.