I read that a battery with a dead cell would not charge above 10.5 volts? However if each cell is 2 volts wouldn’t it be more correct to say a battery with a dead cell will charge up to anything between 10 and 11.9 volts?
Typically, a battery with a dead cell, when fully charged will show the 12.5+vdc as you'd expect. However, once you put it under any type of heavy load (ie: trying to start the vehicle), the voltage will drop down to ~10.5vdc. There is usually a small amount of charge in the cell at first, but is soon wiped out after the battery is put to the test.