When charging an empty SLA or AGM, GEL, VRLA battery,the charger output a constant current (C.C.), the battery voltage will increase slowly, when this voltage reaches 14.8V (For 12V battery)  or N*14.8V ("N" means the serial number of 12V SLA battery), it's also called " equalizing charging" or "CVh". At this stage, the battery voltage is limited at N*14.8V and the charging current will declined slowly. When the charging current drop to 0.03C level, the battery will be full charged, the charger will change the CV. value from n14.8V to n13.8V, this stage also called "Floating charging" stage. One variation is to start a timer at "CVh" stage, when the timmer out, the charger will enter "Floating charging stage" automatically. 

(blue-Voltage, white-Current, green-Temperature)

This curve is a real record for a standard 3 stages charging process, based on A100-24 charger.