Dirk I would try the SMC reset again as I don't think you gave the system enough time to discharge fully. Did you follow this Apple TN? [http://support.apple.com/kb/HT3964|Intel-based Macs: Resetting the System Management Controller (SMC)] Some people have found they needed to remove the battery when doing it.
As you are getting SMC telling you the batteries status we know its communicating to the battery so its a working battery and the connector is also functioning. The I/O board does have some of the charging logic on it on this model (4 - FET transistors). So it's possible it is having issues. I would give this little gem of an app a try [http://www.coconut-flavour.com/coconutbattery/|coconutBattery 2.8] to see what the SMC is doing and what its detecting. With its information you should be able to tell if the I/O board is working.
You may have a deeper problem within the main logic board.