Battery voltage drop

Almsot sounds like a shorted cell in the battery. That would drain it down when you stopped and the alternator coudl charge as hard as it could and would not bring the votlage up properly. The 10.89V at the field brush is saying that the low battery votage is prompting the VR to command the alternator to full output.

The other possibilities are:
1) alternator gone bad again
2) something in the wiring between alternator output and battery. Exmaine the alternator output wire carefully for breaks and bad connections, especially where it goes through the firewall. Wiggle each connection and along the wire whiel watching the bettery charging voltage at fast idle and see if it jumps upas you wiggle it anywhere.

Has your ammeter been acting OK, showing 'charge' (needle towards 'C'). It should show some 'C' after starting and then gradually settle back towards the middle as you drive it a while. Constantly being heavily towards 'C' indicates that it is always charging the battery which is typical of a shorted cell.

Disconect the battery and let is set, and take readings every hour and in the morning to see if it is dropping. If yes, then suspect a bad cell. If not, then the battery is not being charged in the car. Re-charge the abtteyr and start over in the troubleshooting process.