The charger will charge the battery until it reaches 14.5 volts, then go into a monitoring mode while reading "FUL" on the display. When the voltage drops back to 12.5 volts, the unit will go into a float mode charge at a two Amp charge rate, while the display will read "FLO" for a short period and the amount of charging will appear on the display.
The unit charges to 13.9/14.0 volts DC during stage one, to 14.3/14.5 volts DC during stage two, and to 13.7/13.8 volts DC during stage three. Your unit will not display "FUL" or show charging complete until these levels have been attained.
By disconnecting the unit and reconnecting the charger, it will read full if it reads approximately 12.7 volts DC or greater.
There is approximately a two minute delay for the maintainer to turn on. The time taken by the charger during these steps varies depending on the battery's condition. Sulfation is a battery's biggest enemy.