Engineering battery packs for safety and reliability

Typically, packs consist of more than 100 components, generating 50–204 kilowatt-hours at around 300 volts.

Battery technologies have evolved from early lead-acid cells used in storage to nickel-cadmium, nickel-metal hydride and polymer batteries. This has today culminated in lithium phosphate and sodium-ion chemistries that dominate modern applications. In a Battery Energy Storage System (BESS), the battery pack is the most critical component supported by advanced cooling and safety systems. Earlier, a 20-foot container could deliver 2–3.5 MWh capacity, but technology is advancing toward compact five-megawatt-hour energy boxes. Achieving this requires integrating both an HVAC system for the container and a dedicated liquid cooling loop, often water-glycol-based, for the battery packs. Effective thermal management, along with multiple sensors, ensures safe operation and reliable performance. At the core lies the Battery Management System (BMS), which monitors cells, manages charging and discharging and safeguards against faults. The BMS communicates seamlessly with the broader Energy Management System (EMS), which ensures efficiency, safety and longevity of grid-scale storage assets.

Inside the battery pack

Battery packs operate across diverse voltages, currents, powers, energies and environmental conditions. It operates with critical factors including fault tolerance, redundancy, health monitoring, electrical interfaces, thermal management and safety. It is built hierarchically, starting with cells assembled into modules, which then form a battery pack.

In large-scale systems, a 5 MWh container module is arranged in racks. Within each pack, sensors monitor voltage and temperature, while thermal management systems with cold plates regulate heat. A battery disconnect unit integrates coolant ports, a battery management system (BMS), recharge components and wiring harnesses. Typically, packs consist of more than 100 components, generating 50–204 kilowatt-hours at around 300 volts. Proper arrangement of prismatic cells is crucial for maximising energy within given dimensions. However, challenges remain: India relies heavily on neighbouring countries for raw materials and components. This makes supply chain resilient, manufacturing flexibility and strict adherence to quality standards essential for growth.

Thermal management system

A thermal management system is important in batteries. A fading capacity due to an electrolyte and electrodes can lead to internal imbalance, loss of mechanical stability and increased impedance.

You can utilise various simulation software and testing results in your lab to test each cell before submitting it for testing and validation, which ensures accurate results. Ignoring tests can cause problems, also leading to fire. For example, there was one case in Europe where a 2.5-megawatt-hour container caught fire, and it was burning for five days. Due to cheaper tendering, low-quality cells are often selected. In large packs with over 5,000 cells, even a single imbalanced cell can reduce capacity, forcing the BMS to impose control limits. This leads to efficiency losses and potential risks. Hence, cell selection must not be based on cost alone. Thermal and electrical stability are equally critical to ensure reliability, safety and long-term performance of the battery system.

Certifications

Certification is a must for deploying safe and reliable energy storage systems. Standards such as UL 1973, UL 9540, UL 9540A, and IEC 62619 apply to different applications, covering batteries, inverters, converters and complete containers. At the container level, UL 9540 is mandatory as it outlines testing procedures for fire incidents, while rack-level systems require UL 1973 and UL 1743. Pack-level certifications are equally essential, since without them, containers cannot be deployed in the field.

However, achieving complete container-level UL certification in India is not currently possible, which poses a major challenge for manufacturers. In addition to hardware standards, the evolution of software and compliance with functional safety requirements are vital to ensure overall system safety and performance. Manufacturers must navigate multiple certifications across UL and IEC frameworks to meet global benchmarks that assure product quality, ultimately building trust in large-scale energy storage deployments. Without the proper certification, one can’t put a container in the field.