Generally, the charger enters the float stage as early as when the battery capacity reaches 85%. with some exceptions of 95%. The voltage will start to taper down while maintaining a constant. level. The battery becomes fully charged during this state and maintains a 100% charge indefinitely. The current will slowly decrease until it is considered a trickle in the float stage. It is where the name "trickle charger" is derived from. In short, a low stream of current is going into the battery continuously but only at a safe rate so as to achieve a constant full charge of the battery. It has been certified safe to leave the charger on in the float mode for months on end even though the majority of the battery chargers would be turned off at this point. It is actually a healthy practice for a battery to be at 100% stage of charge.