Current sense
Current Sense uses battery current data that is measured by the battery monitor shunt (requires a BMV or SmartShunt) and provides it to the charger, the charger then references this current data (as opposed to the charger output current) for the tail current setting.
The tail current setting references the diminishing level of charge current (typical at the end of a full charge cycle) in relation to the trigger threshold to determine when the battery is fully charged and consequently when the absorption stage can be ended (prior to the absorption stage time limit being reached). The use of tail current to end absorption stage is a highly effective and common method used to properly charge lead acid based batteries.
In order to end the absorption phase at the correct point, it is important that the true current flow into the battery is referenced in relation to the tail current threshold, rather than the charger output current which may be significantly higher; if any loads are powered while charging a portion of the charger output current will be flowing directly to the loads, making the tail current condition more difficult or impossible to meet without current sense.