Maldonado is in the conversation for the worst-hitting everyday player of the postwar era (of players with at least 3,000 PA, he has the second lowest batting average to Jeff Mathis, but Mathis never caught more than 100 games in a season; he is tied for 25th in lowest wOBA; the one thing that maybe elevates him from absolute worst is that when he happens to make contact, he hits with more power than most of the other guys in the basement).
Anyway, anyone expecting him to make any contribution at all with his bat is missing the point. That's not why he's there. From an outsider's perspective, it looks like it's an easy position to upgrade, but I think this is an area where you just have to roll with how the team values him, especially given that a catcher's defensive contributions are still difficult to quantify.
I also don't think that there's any point in adding another catcher at this late stage, even if Maldonado can't catch 100 games. They need to see what Lee and/or Diaz can do, and no one available today is likely to offer an upgrade over them even if they aren't very good. If it's a real problem as the season goes on, they can add a catcher at the deadline like they did last year.