When charging, batteries there are three charging stages. The first stage is the constant current charge, and typically takes about half of the total time required to reach a fully charged state. A battery is typically charged to 70% of the fully charged state during the constant current charge. During this state, voltage is typically increasing while current remains constant. The second stage is the topping charge. The voltage is relatively constant, typically between 2.4V and 2.45V per cell. This is very likely the 14.4v you are seeing. During the topping charge, voltage peaks and current decreases. The battery remains in this state, until the remaining 30% of charging is completed. Frequently, this is referred to as saturation. Once the batteries reach saturation or full charge, the third stage of charging (float charging) is entered. During float charging, both voltage and current are reduced. Float voltages vary depending on the type of cell (Gel 13.05V, Flooded 13.4V and AGM 13.6V).