Wijnand,
Have you made any progress on this issue since your last post? Unfortunately, I am not here to provide ideas, but to share in your frustration.
I have the same problem with my MacBook 2.16 Core 2 Duo system. Will not read the battery, although battery is fully charged, works elsewhere, and is recognized by Coconut Battery. System works fine when plugged in with the power adapter; green mag light is on.
Since it works with the power adapter, it's more of a nuisance than anything.
Thanks to all who have helped!