Bush is right.
The detection is on the battery bus which is powered even if the battery is flat.
Protection is on the hot battery bus wich bets unpowered in the battery is dead.
Therefore if the charger fails and the battery gets flat one has detection but no protection.
I don't know how it is in the 737NG but on the classics (300-500) it was like that, cant imagine it is any different on the NG's