In reality, float voltage measurements are of limited value. They can be used to confirm that the charger is working, but they give no information at all about the battery's state of health. Measuring the float voltage of a cell will also show whether or not it is fully charged, but it is important to remember that, just because a cell is fully charged, this doesn’t mean that it will deliver full capacity. It is by no means unusual for a battery that is close to failure to have a float voltage that is within acceptable limits.
A low float voltage may indicate that there is a short in the cell. In a lead-acid battery, this should be suspected if the float voltage is 2.06 V or less, assuming that the charger is set for 2.17 V per cell. In other cases, a cell may float at a considerably higher voltage than average. This may be because the high float voltage cell is compensating for another weaker cell that is floating low. It is also possible for one cell to float high to compensate for several cells that are floating a little low, because the total of all the cell float voltages must always equal the charger setting.