# BMS Source: https://ordergroup.co/glossary/bms/ Last updated: 2026-10-10 > Battery management system (BMS) explained for software buyers: what it measures, how it differs from EMS, EU battery data rules and what to require. [Energy](https://ordergroup.co/glossary/energy/) 4 min read # BMS Battery management system Also known as: battery management system Definition A battery management system (BMS) is the electronics and software that monitor a battery's cells, including voltage, temperature and state of charge, balance them and disconnect the battery when it leaves safe limits. In buildings, BMS can also mean a building management system. Cite this entry Text "BMS". Order Group, Software glossary, 10 October 2026. https://ordergroup.co/glossary/bms/ HTML `BMS - Order Group` Reviewed by [Michał Dżaman](https://ordergroup.co/authors/michal-dzaman/), Co-founder & Head of Backend Last reviewed 10 October 2026 ## How a BMS works A battery management system is the layer that keeps a battery safe and tells the rest of the system what state it is in. It sits in or next to the battery pack, usually as embedded hardware and firmware from the battery manufacturer. In a large storage system it is a hierarchy: a controller per module reads the cells, a rack controller combines the modules, and a system controller reports the whole battery to the outside world. Its main functions: - Measurement. Cell voltages, temperatures and pack current, read continuously. - Estimation. [State of charge](https://ordergroup.co/glossary/state-of-charge/) (SoC) and state of health (SoH) cannot be measured directly. The BMS estimates them from current counting, voltage at rest and a model of the cells. - Balancing. Cells drift apart over time. The BMS evens them out, either by bleeding energy from the fullest cells as heat (passive balancing) or by moving energy between cells (active balancing). - Thermal management. It watches temperatures and triggers cooling, heating or a power reduction before a cell leaves its window. - Protection. When a hard limit is crossed, the BMS opens the contactors and isolates the battery. It also reports the charge and discharge power the battery can accept right now, which shrinks when the battery is cold, nearly full or nearly empty. - Communication. It passes SoC, limits, alarms and measurements to the systems above it, usually the power conversion system and the energy management system. The acronym has a second meaning. In facilities, BMS stands for building management system, the control system that runs heating, ventilation, air conditioning, lighting and access in a building. The idea is similar, one control layer over many devices, but it is a separate field with its own vendors and protocols. This entry is about the battery sense. BMS, EMS and SCADA compared QuestionBMSEMSSCADA What does it answer?Is the battery safe and what is its state?What should the battery and the site do now?What is happening across the plant, and what does the operator want?Time scaleMilliseconds to secondsSeconds to hoursSeconds to daysWhere it runsIn or next to the battery packEdge device at the site, with the cloud for historyControl room or web platformUsually supplied byBattery manufacturerIntegrator, software house or battery vendorAsset owner's platform or integrator ## What a BMS means for your software Few projects write BMS firmware. Most buy a battery with a BMS inside and build the software that talks to it: an [EMS](https://ordergroup.co/glossary/ems/), a monitoring platform or a fleet dashboard. The BMS then becomes an interface you do not control, and that is where the requirements come from: - The BMS limits are hard constraints. The EMS reads the allowed charge and discharge power in every cycle and stays inside it. It keeps the battery in a narrower operating window, so the BMS protection is never the thing that stops it. - Each battery model has its own register map and alarm codes, often over [Modbus](https://ordergroup.co/glossary/modbus/). Ask the battery supplier for the documentation and a contact for communication questions before the integration starts, and plan for a firmware update moving registers. - Every read and write is checked. A failed read must not be published as a fresh value, and the software should read back what it wrote. A battery that reports nothing for a few cycles is an alarm, not a zero. - Alarms are mapped. Hundreds of vendor codes have to become a short list that an operator can act on, with a clear state for a battery that is switched off. - History is kept for the warranty. Temperatures, cycles, deep discharges and SoH estimates decide warranty claims and the battery's resale value, so the platform stores their history. Writing the specification? Add BMS to your requirements checklist Collect the terms your project touches and get their system requirements in one e-mail, ready for an RFP. BMS data the software above it usually reads SignalUsed for State of chargeEvery charge and discharge decision, reserves for commitmentsAllowed charge and discharge powerUpper bound for the EMS setpointCell voltage and temperature extremesAlarms, derating, warranty historyState of healthCapacity planning, warranty, residual valueAlarms and battery statusOperator screens, automatic fallback to a safe mode ## Rules and standards The Battery Regulation (EU) 2023/1542 made holding BMS data a legal requirement. Article 14 requires, from August 18, 2024, that stationary battery energy storage systems, light means of transport batteries and electric vehicle batteries contain a BMS holding data on the parameters that determine state of health and expected lifetime, listed in Annex VII. The person who legally bought the battery, and third parties acting on their behalf, must get read-only access to that data, among other purposes to evaluate the battery's residual value or to prepare it for reuse or repurposing. For a buyer of battery software this has two consequences. The data the BMS holds is no longer only the battery vendor's business, so a platform has a legal basis to read it. And the platform should store it in a form that can be shown to an owner, a buyer of a used battery or an insurer. ## From our projects Our work sits above the cell-level BMS: we build the software that reads it, respects its limits and turns its data into decisions. We have not written BMS firmware for chemical cells. For [Kyoto Group](https://ordergroup.co/case-studies/kyoto-digital-twin-software/) the storage was not a chemical battery but a molten-salt thermal store. In the 2024 phase our scope included what Kyoto calls the BMS of its thermal battery: control of the valves, pumps and the flow of hot fluid in the salt store, integrated with the plant's SCADA layer. Next to it the team built surveillance with infrared cameras and image recognition that works with the BMS and SCADA to catch anomalies a single sensor would miss. The EMS we built for [Skyfri](https://ordergroup.co/case-studies/skyfri-solar-asset-management-platform/) started with communication workshops with the battery supplier in February 2024 and treats the limits the battery reports as hard constraints. For Global Green's battery storage sites we mapped the registers of battery systems from two manufacturers in 2026 and added an alarm for a battery in the off state in July 2026. Testing found a failed batch read that published stale values as fresh, which was fixed. In [Zeronest's](https://ordergroup.co/case-studies/zeronest-solar-panel-monitoring-app/) EMS the battery is reached through the inverter, so the minimum and maximum SoC come from the inverter model and can be overridden for each installation. From our projects [Skyfri - Solar & Battery Asset Management Platform How Order Group built the fully offline EMS behind Skyfri's solar platform, which controlled more than 5 MWh of battery storage across 7 live plants.](https://ordergroup.co/case-studies/skyfri-solar-asset-management-platform/) ## Related terms - [BESS](https://ordergroup.co/glossary/bess/) Battery energy storage system A battery energy storage system (BESS) stores electricity in rechargeable batteries and releases it to a site or the grid on command. It combines battery racks, a battery management system, power conversion equipment and control software. - [EMS](https://ordergroup.co/glossary/ems/) Energy management system An energy management system (EMS) is software that reads the meters, inverters and batteries on a site and sends them setpoints, deciding when to charge, discharge, curtail or trade within grid, contract and safety limits. - [State of charge (SoC)](https://ordergroup.co/glossary/state-of-charge/) State of charge (SoC) is the energy available in a battery, expressed as a percentage of its rated capacity. The battery management system estimates it, and energy software uses it to decide when a battery may charge, discharge or hold a reserve. - [Thermal energy storage](https://ordergroup.co/glossary/thermal-energy-storage/) Thermal energy storage (TES) stores energy by heating or cooling a medium such as water, rock or molten salt, and releases it later as heat, cold or power. It lets a site buy electricity when it is cheap and deliver heat when it is needed. ## Read more on the blog - Article [Battery Energy Storage System (BESS): How It Works and What Software It Needs](https://ordergroup.co/blog/battery-energy-storage-system/) - Article [What Does BMS Mean? Battery & Building Management Systems Explained](https://ordergroup.co/blog/what-is-bms/) - Article [Get More Out of Cognite Data Fusion](https://ordergroup.co/blog/cognite-data-fusion-guide/) - Article [Managing Surplus Renewable Energy with Energy Storage Systems](https://ordergroup.co/blog/surplus-renewable-energy-storage/) ## Sources 1. [Regulation (EU) 2023/1542 concerning batteries and waste batteries, Article 14 and Annex VII](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32023R1542) - EUR-Lex Michał Dżaman reviewed this entry. Ask how it applies to your project. [Ask an engineer](https://ordergroup.co/contact-us/) ## FAQ ![Michał Dżaman](https://ordergroup.co/media/images/T02DHCC1Z-USU629221-c8b7d6d66b56-512.format-webp.webp) Michał Dżaman Co-founder & Head of Backend [Talk to an engineer](https://ordergroup.co/contact-us/) ### What is the difference between a BMS and an EMS? A BMS protects the cells of one battery and reports its state and limits. An EMS decides what the whole site does with that battery, the solar plant and the grid connection, and takes the BMS limits as hard constraints. The EMS asks for power; the BMS decides whether the cells can deliver it. ### Who supplies the BMS, and can I replace it? The battery manufacturer almost always supplies it, and its safety approvals and warranty depend on it. Replacing it is rarely an option. What you can choose is the software above it, as long as the BMS exposes its data and limits over a documented interface. ### What data should I require from the battery's BMS? At minimum: state of charge, allowed charge and discharge power, cell voltage and temperature extremes, state of health, battery status and alarms, with documented registers or an API. Under Article 14 of the Battery Regulation, state of health and lifetime data must be available read-only to the owner. ### Does BMS also mean building management system? Yes. In facilities BMS means building management system, which controls HVAC, lighting and access in a building. It shares the acronym but not the technology or the vendors. In energy storage and electric vehicles, BMS means battery management system. Building a system that depends on BMS? See how we build software for this domain, with case studies and the stack we use. [See Energy Hub](https://ordergroup.co/energy-hub/) Requirements checklist For each term we send the definition and what it requires from your software. Free, no sales call needed. Your checklist is empty. Use the plus next to a term to add it.