What is a BMS?
It is a microprocessor based computer loaded with firmware whose design is to be connected to individual lithium blocks (cells) under its management control and to also be connected to the charging source. The BMS contains firmware that has been programmed into it and this firmware in most all cases can be undated. The BMS allows through communication the data on the individual lithium cells that make up the entire battery pack. Both the voltage and the power. Any voltage and power (amperage) coming from the charging source is intercepted by the BMS and only the correct amount of voltage and amps are allowed to pass into the lithium cell. The BMS also knows then to cut out the lithium cell if the voltage is too high or too low to prevent failure. Some BMS have temperature sensors programmed to control the charge going into the cell or even to heat the cell up with an onboard heater. So the BMS is really a Battery Management Computer and it is inside the "battery chassis" along with all of the cells.
Closed loop means that the inverter and the BMS can communicate with each othr passing information about each cell and charging in a continuing intelligent way and present the data to the human user such as the battery temperatures and state of charge, the voltage in and out and the power in and out of the batteries. Once connected and working, the human user just really needs to know their cut out and cut in voltages for both high and low or even just what Status of Charge they want to use during the day.
Manually entering parameters for the battery into the charger provides the guide for voltage and amperage that the charger will present to the lithium battery pack. BUT, the onboard BMS will intercept, block, allow as is permitted by its programming to charge and discharge the batteries. What is not available is the complete accuracy and continuous monitoring of the batteries state that can often be viewed via the internet with a closed loop system. Also, it is best in manual mode to program the battery parameters using voltages rather than the state of charge.