My 19.2 charger is showing that the batteries are fully charged when they are put in and I know they are low. Is it the charger or the batteries?
It'd be good if you can monitor the battery voltage while in the charger by using two very thin wires or tin foil strips to bring out the battery terminals to where you can measure them.
Probably the internal resistance of the batt is very high because it's bad and so the charger thinks it is charged.
The batt can be checked for excessive internal resistance with a resistive load and a voltmeter if you have batt specs or another known good batt to check it against.
What battery technology? Nicad, Li-ion. . .?