This state occurs almost exclusively when the battery is not loaded, as trickle charging will not keep a battery charged if current is being drawn by a load.
[1][2] A battery under continuous float voltage charging is said to be float-charging.
In such cases, the trickle charging equals the energy expended by the lead–acid battery splitting the water in the electrolyte into hydrogen and oxygen gases.
In that case, supervisory circuits (sometimes called battery management systems) adjust electrical conditions during charging to match the requirements of the battery chemistry.
For Li-ion batteries generally, and for some variants especially, failure to accommodate the limitations of the chemistry and electro-chemistry of a cell, with regard to trickle charging after reaching a fully charged state, can lead to overheating and fire or explosion.