Battery monitoring systems

A battery management system (BMS) is an electronic circuit for monitoring and controlling an array of rechargeable battery cells – a rechargeable battery. The term is not a fixed definition and is used for simple charge state detection as well as for highly complex systems with data interfaces and extensive power electronics. The need for a BMS results from the interconnection of several batteries to a battery. The BMS is intended to recognize, monitors and corrects the unavoidable production-induced scattering of various parameters of the batteries such as capacitance and leakage currents. Operational data are also displayed partly or stored for service purposes.


BMS is also used in marine battery monitors. Such monitors are used on ships and boats to control the battery usage, battery level and consumption of the battery. BMS can be found in various interconnections of accumulator cells, for example traction batteries of electric cars, uninterruptible power supplies or notebooks.

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The simplest form is a charger with a few cells. However, modern systems monitors often have complex controls that individually monitor all series-connected accumulator cells and provide information about their condition. One of the major challenges of the monitoring is the determination of the charge state, which is difficult to determine in many battery types.


In the mass market, battery managementand monitoring systems became increasingly relevant in the course of ever-decreasing electronic power components and with the advent of lithium-based accumulators. In these types of batteries, the charging states of the individual cells must be kept within very narrow limits in order to avoid breakdowns and further damage up to the risk of fire of the rechargeable battery. At the same time, the display of the battery status or operating time was significantly improved by the electronics now available.

Functions of battery management systems

Simple BMS for 4-cell rechargeable battery: short-circuit protection, single-cell monitoring against over- and undervoltage, balancer


Standard functions for battery management systems, land battery monitors or marine battery monitors can be:


-cell protection

-charge control

-load management

-Determination of the charge state

-Determination of “cell health” (aging, residual capacity, internal resistance, etc.)

-Balancing the cells


-Authentication and identification


-thermal management

-Amp power usage

-current monitoring




After the life of the cells is lower than that of the vehicle and to enable the customer to choose from several competitors, a standardized interface from the battery manageing and monitoring system to the vehicle would be desirable. This could lead to the development of cell chemistry independent of the integration of the Lademanagement into the battery management and monitoring system.

Battery monitor or battery managenent system allows the tracking of data such as

-The maximum load current (CCA)

-The maximum discharge current (DCL)

-The energy supplied since the last load or last charge cycle

-The total energy used since the first use

-The total operating time since the first use

-Battery protection

A BMS protects its battery by preventing it from operating outside its typical operating range:


-Over-voltage (when loading)

-Undervoltage (during discharge), particularly important for lead-acid and Li-ion cells


-Under temperature

-Overpressure (NiMH batteries)


The battery monitoring and management system prevents the battery from operating outside its typical operating range by:

-An internal switch

-Devices external to the battery that reduce or terminate its use

-Control of the environment, by radiators, fans, air conditioners or liquid refrigerants