So after playing around with the Vaio and logging a service call about the numlock issue I found that no matter what I did the notebook would only charge the battery to 80%. Since I had ordered a high capacity battery as well I put that one into the notebook to find the exact same behaviour. Charged to 80% and off. Both Vista an Opensolaris reported the notebook was running on mains, battery connected, charged to 80% neither charging or discharging.
Time for another service call.
By now it was day 4 (in words four) after I logged the call about numlock.
And finally some kind soul from Sony's Vaio support answered to the numlock question. Indeed there is no such option in the BIOS (that much I knew already). There also is no way to turn off numlock at bootup using any other tool (Vaio Control Center may be). No BIOS update available. So here I am stuck with a turned on numlock on every boot and it takes Sony's support 4 days to find that out. Great work!
"Only" two days after logging the call on the battery question Vaio Support reacted and asked me a lot of questions. Yes this is the original power supply and batteries that Sony shipped. Yes my power outlet works just fine (why would the notebook run on mains otherwise?). Yes the power supply gets warm after being plugged in for a while. I tried both batteries as well. The guy then suggested a nice list of things to try (I was waiting for "dance around naked" until the end...) No real solution suggested though as I already had all cables removed and reinserted etc.
Funny I had a look around in the "Vaio Control Center" that comes installed with Vista. There is an option to extend battery life by only charging the battery to 80%. This was of course enabled. Switched off I have fully charged batteries.
And of course tech support didn't come up with the thing to check. But it has been only two days on this call.
Let's see how my other calls go. 2 more open for 2 days now.