The battery charger is a component that generates a constant voltage and current based on the type and number of battery cells to ensure proper charging operations. On the other hand, the Battery Management System (BMS) is responsible for managing and preventing damage to the batteries, and it does not handle the charging process.
For example, if you connect an adapter with a voltage of 12 volts and a current of 2 amps to a pack of 2 lithium batteries (assuming a model of 1000mAh each) with a BMS for 2 cells, the BMS will immediately interrupt the charging process due to Over-Voltage Protection. It will disconnect the connection between the battery and the adapter.