Besides the usual plus and minus terminals, it also has two or more terminals to connect to the BMS; typically minus is also used as BMS "ground". BMS interface examples are: SMBus, PMBus, EIA-232, EIA-485 and Local Interconnect Network.
The smart battery can internally measure voltage and current, and deduce charge level and SoH (State of Health) parameters, indicating the state of the cells.
Externally the smart battery can communicate with a smart battery charger and a smart energy user via the bus interface. The smart battery can demand that the charging stops, ask for charging, or demand that the smart energy user stop using power from this battery.
There is one standard specification for smart batteries, called Smart Battery System and many ad-hoc specifications.