Float Stage (Maintenance Charge)
The holding stage applied after the battery is full, at a voltage low enough only to cover the self-discharge. For 12 V lead-acid it is typically held in the 13.4–13.8 V range, and the battery can be held at this voltage for months.
Every battery discharges by itself even when nothing is connected; in lead-acid this loss is of the order of a few percent per month. The float voltage covers exactly this loss. If the value is chosen correctly the battery neither discharges nor loses water by gassing.
A float voltage that is too high produces insidious damage: the battery stays permanently in slight overcharge, the electrolyte evaporates slowly and in sealed AGM or gel batteries this water cannot be replaced. Too low a value, on the other hand, leaves the battery to sulphate within months. Good chargers correct the float voltage according to ambient temperature.
In an RV the float stage comes into play especially in winter storage. If the vehicle is left plugged in, the charger holds the battery at float voltage. In LiFePO4 packs, however, most manufacturers do not want a continuous float applied; storing the pack at around half charge and cutting the charge at the end of absorption is recommended. This difference makes the chemistry selection on the charger important.
Context in which this term is used: RV automatic levelling guide