Pre-Morrison's Uberbat, Batman was probably the best example of "believably smart," at least as far as leading characters go.
Sure, he was a Sherlockian detective, but he wasn't infallible. He needed to gather clues, follow up on dead ends and even get assistance at times (and I dont mean from magic hacker Oracle, I mean that he would [for example] have "Bruce Wayne" drop in on someone with relevant information or some such thing). And, while he was usually depicted as the smart guy in the Justice League, he wasn't the deux ex machina he was later turned into. The Flash (a police scientist), the Atom (an Ivy league physicist) or Superman (super-intelligence) were as likely to make the big discovery.
Batman was a guy who followed clues better than anyone else, not Einstein.
