Finding
The BMS is now regulated safety equipment as well as a range estimator, and the protection hardware around it is where Chinese suppliers have caught up fastest
China's GB 38031-2025, mandatory for new type approvals from July 2026, requires that a pack does not catch fire or explode after a cell goes into thermal runaway, and the EU Battery Regulation requires state-of-health data to be readable from the BMS. Cell monitor chips come mostly from Analog Devices, Texas Instruments, NXP, Infineon, ST and Renesas; contactors and pyrofuses increasingly come from Hongfa and Xi'an Sinofuse in China.
A BMS measures every cell's voltage and temperature, the pack current and the insulation between the high-voltage system and the chassis; estimates state of charge (SOC), state of health (SOH) and the power the pack can deliver or accept; and opens the contactors when a limit is crossed. Monitor chips (analog front ends, or AFEs) sit on each module and report to a pack controller over an isolated daisy chain or, in GM's Ultium packs, by radio using Analog Devices' wireless BMS. Some automakers call the pack controller the battery control unit (BCU) and reserve BMS for the monitoring layer; in zonal vehicles the BCU functions can move into a central or zonal computer, covered in Battery Control Units.
Cell-to-pack designs - BYD's Blade pack and CATL's Qilin - remove the module, so monitoring moves onto flexible circuits and cell contact systems laid across the cells. Tesla, BYD, GM, Rivian and the Chinese cell makers write their own BMS software, because SOC accuracy sets usable range and SOH estimates set warranty cost. Most monitor chips are made in the chipmakers' own analog fabs; Texas Instruments builds analog chips at its Sherman, Texas fabs.
The protection hardware at the pack output - the battery disconnect unit with its contactors, precharge relay, fuses, pyrofuse and current sensor - is a separate supply chain from the BMS electronics. Hongfa is the world's largest relay maker and a leading high-voltage contactor supplier to Chinese automakers; Xi'an Sinofuse supplies EV fuses and pyrofuses in volume. Western suppliers lead in pyrotechnic switches from airbag makers Autoliv and Daicel and in precision shunts and Hall sensors from Isabellenhuette, LEM and Melexis.
Functions
What the BMS Does
Every function below runs continuously while the pack is connected, and most must meet ISO 26262 safety integrity levels up to ASIL C or D.
| Function | What it does | Hardware involved |
|---|---|---|
| Monitoring | Cell voltages and temperatures, pack voltage and current | Monitor chips (AFEs), thermistors, shunt or Hall current sensor |
| State estimation | SOC, SOH and available power (SOP) for charge and discharge | Pack controller MCU and software models |
| Protection | Over- and under-voltage, over-temperature, overcurrent and short circuit | Monitor chips, current sensor, contactors, fuses, pyrofuse |
| Contactor control | Precharge sequencing, connection and disconnection of the HV bus | Contactor drivers, precharge relay and resistor |
| Balancing | Equalizes cell charge to keep usable capacity; passive (bleed resistors) or active (charge transfer) | Balancing circuits in the monitor chips |
| Isolation monitoring | Detects leakage from the HV system to the chassis | Isolation monitor in the BMS or the disconnect unit |
| Thermal coordination | Sets cooling and heating targets and derates power | Link to the thermal management system |
| Diagnostics and data | Fault logs, service data, state-of-health records, over-the-air updates | Pack controller, gateway, telematics |
Architectures
Centralized, Distributed and Wireless BMS
Topology follows pack design: large module-based packs went distributed, cell-to-pack designs flatten the sensing layer, and wireless removes the daisy-chain harness.
| Architecture | What it looks like | Benefit | Trade-off | Examples |
|---|---|---|---|---|
| Centralized | One controller wired directly to every cell tap | Fewest boards; low cost for small packs | Long sensing harness; scales poorly | Small packs, two-wheelers, early EVs |
| Distributed (modular) | Monitor board on each module, daisy-chained to a pack controller | Scales with pack size; short sensing runs | More boards and isolated links | Most module-based packs |
| Wireless | Module monitors talk to the controller by radio | No daisy-chain harness; simpler pack assembly and reuse | Radio qualification and cybersecurity | GM Ultium (Analog Devices wireless BMS) |
| Cell-to-pack sensing | Flexible circuits across cells feed monitor chips on a few boards | Fewer parts; denser packs | Repair is harder; tight thermal coupling | BYD Blade, CATL Qilin, Tesla structural pack |
Pack electronics
Battery Electronics Beyond the BMS
The disconnect unit and its parts connect the pack to the vehicle and cut it off in a fault. Several are crash-safety parts made by airbag and fuse suppliers rather than by electronics makers.
| Component | Function | Suppliers outside China | Chinese suppliers |
|---|---|---|---|
| Cell monitoring ICs (AFE) | Measure each cell's voltage and temperature; run balancing | Analog Devices, Texas Instruments, NXP, Infineon, STMicroelectronics, Renesas | Novosense; BYD Semiconductor |
| Pack controller MCU | Runs BMS software at ASIL C or D | Infineon (AURIX), NXP (S32K), Renesas, ST, TI | Chipways |
| Battery disconnect unit (BDU) or junction box | Houses contactors, precharge, fuses and current sensor at the pack output | Eberspaecher, Lear, Aptiv, Yazaki, Sumitomo Electric, TE Connectivity | Built in-house by BYD and CATL |
| HV contactors and precharge relays | Connect and isolate the pack from the HV bus | TE Connectivity, Panasonic, Sensata (Gigavac) | Hongfa, Kunshan Guoli |
| Pyrofuses and pyro switches | Cut the HV circuit within milliseconds in a crash or hard short | Autoliv, Daicel, Mersen, Eaton, Littelfuse | Xi'an Sinofuse |
| HV fuses | Overcurrent protection for the pack and auxiliary loads | Mersen, Littelfuse, Eaton (Bussmann), Pacific Engineering | Xi'an Sinofuse |
| Current sensors and shunts | Measure pack current for SOC and protection | LEM, Isabellenhuette, Melexis, Allegro, Infineon, Sensata | Novosense |
| Isolation monitors | Detect leakage between HV and chassis | Bender; functions built into BMS chips | Built into domestic BMS designs |
BMS suppliers
Who Builds the BMS
Most volume BMS hardware and nearly all BMS software is designed by automakers and cell makers; Tier 1s supply the rest. Pack thermal systems and onboard chargers are covered on their own directory pages.
| Company | Type | HQ | What it supplies | Key customers |
|---|---|---|---|---|
| Tesla | Automaker in-house | US | Pack BMS and module monitor boards | Tesla |
| BYD (FinDreams Battery) | Automaker in-house | China | BMS for Blade packs | BYD brands; FinDreams pack customers |
| General Motors | Automaker in-house | US | Wireless BMS on Analog Devices chips (Ultium) | Chevrolet, Cadillac, GMC; Honda Prologue |
| CATL | Cell and pack maker | China | BMS supplied with CTP and Qilin packs | Zeekr, Li Auto |
| LG Energy Solution | Cell and pack maker | South Korea | BMS hardware and battery diagnostics software | - |
| Preh (Joyson Electronics) | Tier 1 | Germany (owned by China's Joyson) | BMS controllers and cell supervision boards | BMW |
| Bosch | Tier 1 | Germany | BMS controllers and software | - |
| Aumovio (formerly Continental Automotive) | Tier 1 | Germany | BMS and pack sensors | - |
| Marelli | Tier 1 | Japan | BMS including wireless BMS | - |
| Sensata (Lithium Balance) | Tier 1 | US | BMS for commercial, off-highway and stationary packs | - |
| Ligoo | Tier 1 | China | BMS for passenger and commercial EVs | Chinese automakers |
Sources
Sources and scope
- Scope
- EV Battery Management Systems
- Sources
- GB 38031-2025; EU Regulation 2023/1542; ISO 26262; Analog Devices, Texas Instruments, NXP, Infineon, Hongfa, Sinofuse and automaker disclosures
- Updated
- October 2026