Battery Management System (BMS)
The electronic protection unit that monitors the voltage of every cell, the pack current and the temperature in a lithium battery pack and disconnects when a limit is exceeded. It also has the task of balancing the voltage difference between cells, and its use is mandatory in LiFePO4 packs.
A BMS provides four main protections: overcharge, over-discharge, overcurrent and temperature limit. When one of them is exceeded it opens the pack output through a MOSFET or contactor. What the user sees is usually this: the battery suddenly stops delivering current and recovers a short while later.
The second task is balancing. Four LiFePO4 cells in series drift to different voltages over time; the highest cell ends the charge early and the lowest cell cuts the discharge early. The BMS aligns the pack by discharging the full cells through a small resistor.
In an RV the current limit of the BMS directly affects the system design. If the levelling jacks, the inverter and the water pump run at the same time, the total current can exceed the BMS threshold and the pack is cut off unexpectedly. In addition, most BMSs block charging at low temperature; solar or alternator charging not coming on in winter is usually not a fault but this protection working.
The context in which this term is used: RV automatic levelling guide