Sensors - Battery Design

Sensors are used throughout the battery system, but they do not all serve the same purpose or the same audience. A temperature sensor on a cell in a finished pack, a conductivity probe on a formation line, and a pressure transducer in a coolant circuit are all “battery sensors” — but they operate in different contexts, are specified against different requirements, and are the responsibility of different engineering disciplines.

This page provides an overview of the three contexts in which sensors appear in battery systems. Each has its own page where the detail lives.

BMS Sensors

The Battery Management System requires a continuous stream of real-time measurements to protect the cells, estimate state, regulate charging, and control thermal management. These are operational sensors — they are active throughout the life of the pack and their outputs feed directly into the BMS algorithms.

The core BMS sensor set covers:

Cell voltage — the fundamental measurement for state of charge, imbalance detection, and protection
Pack current — for coulomb counting, overcurrent protection, and power limit calculation
Cell temperature — for charge/discharge limit enforcement, thermal management, and lifetime modelling
Pack voltage — as a cross-check and for power electronics interfaces
Isolation resistance — to confirm the high-voltage system remains isolated from chassis ground
Earth bonding impedance — to verify the protective earth connection
Humidity — to detect moisture ingress before it causes damage
Pressure and force — to detect cell swelling and gas generation
Gas sensing — for early warning of thermal runaway
Coolant temperature and flow — to monitor and verify the thermal management circuit
Dielectric strength of coolant — to detect contamination in non-conductive cooling fluids

Some of these are direct measurements; others are estimated using models and sensor fusion. The distinction between hard sensors (physical measurements) and soft sensors (model-based estimates) is an important one in BMS design.

For full coverage of each sensor type, technology options, placement strategy, redundancy, and the role of virtual sensors, see BMS Sensors.

Thermal System Sensors

In liquid-cooled battery systems, the thermal management circuit has its own sensor requirements that sit alongside — but are distinct from — the BMS sensor set. Coolant inlet and outlet temperatures, flow rate, and circuit pressure are monitored to verify that the cooling system is performing correctly and to detect faults such as pump failure, blockage, or coolant loss.

In some architectures these sensors report to a dedicated thermal management controller rather than the BMS directly, but the BMS must receive the data to make correct protection and power limit decisions. The boundary between BMS and thermal management is a system design choice that varies between programmes.

Manufacturing Sensors

Battery manufacturing relies on a separate set of sensors and measurement systems used during production rather than in the finished product. These are process sensors rather than product sensors, and they serve quality assurance and process control functions rather than operational protection.

Manufacturing sensing covers areas including:

Formation and ageing — current and voltage measurement during initial charge/discharge cycles to characterise each cell and establish its baseline
Dimensional inspection — checking cell and module geometry against tolerance, and detecting swelling or deformation that indicates a production defect
Leak testing — verifying seal integrity of cells, modules, and pack enclosures before they leave the line
End-of-line electrical test — isolation resistance, earth bond, and functional checks on the completed pack

This is a distinct engineering discipline from BMS or pack design, and the sensors used are typically integrated into automated test equipment rather than embedded in the product. Manufacturing sensing will be covered in a dedicated page in a future update.

Smart Sensors and the Future

Research is ongoing into embedding sensors directly within the cell during manufacture. A smart battery cell would have the ability to measure key internal variables — electrode potentials, current, temperature, mechanical stress, and internal pressure — and report them without adding complexity to the external pack design.

This would allow the BMS to access information that is currently either unmeasurable or only estimable through models, including internal temperature distribution, local electrode potential, and mechanical state at the cell level. Wireless or powerline data transfer approaches are being explored to integrate these measurements without adding conventional wiring.