How to Find a Manufacturer That Can Do Custom BMS Firmware

How to Find a Manufacturer That Can Do Custom BMS Firmware

TL;DR: Finding a manufacturer that can do custom BMS firmware requires more than searching for “OEM/ODM battery supplier." You need a manufacturer with in-house BMS or PCBA engineering who can document protocol support, firmware version control, validation evidence, and production traceability. Before contacting suppliers, determine whether you need parameter programming, protocol customization, or true firmware development. Then use the RFQ checklist and red-flag list in this guide to separate real capability from vague promises.

Many battery suppliers advertise custom packs. Fewer can actually modify the software running inside the battery management system. This is the core problem buyers face when trying to find a manufacturer that can do custom BMS firmware: the phrase “custom" covers everything from changing a voltage threshold to writing new embedded code, and most supplier websites don’t clarify which version they offer.

This guide defines what custom BMS firmware actually means, breaks it into three levels of complexity, explains which type of supplier fits each level, and gives you exact questions to ask before spending money on samples or tooling.

If you already know your battery specs and communication requirements, you can submit your requirements for engineering review.

What Is Custom BMS Firmware?

A battery management system (BMS) is the combination of hardware and software that monitors, protects, and manages a rechargeable battery pack. NHTSA describes EV battery packs as interconnected cells with hardware and software that manage battery operation, referred to as the BMS.

Custom BMS firmware means modifying the software behavior of that system so the battery works correctly and safely with a specific cell chemistry, pack layout, charger, inverter, controller, display, or host device. It can involve changes to protection thresholds, cell balancing, SOC/SOH calculations, communication protocols, fault handling, sleep/wake logic, data logging, charger handshake behavior, and firmware update processes.

The word “custom" is used loosely in this industry. A supplier might call a label change “custom." They might call reprogramming a single voltage parameter “custom firmware." Or they might mean rewriting embedded C code for a proprietary state machine. These are very different things, and confusing them is where sourcing mistakes begin.

For a deeper look at BMS terminology and specification basics, the guide on what a custom BMS is covers the fundamentals.

Custom Firmware vs. BMS Parameter Settings: Three Levels

Before you search for a manufacturer with custom BMS firmware capability, figure out which level of customization your project actually requires. Most buyers overestimate or underestimate what they need.

Level 1: Parameter Programming

The supplier changes values inside an existing smart BMS without modifying any code. Typical adjustments include overcharge voltage, over-discharge voltage, continuous and peak current limits, temperature cutoffs, cell count, balance start voltage, battery capacity, and Bluetooth name.

This is enough for standard packs where the host system doesn’t require unusual communication behavior. The risk is that a supplier may call this “custom firmware" when no code has been changed at all.

Tools like Texas Instruments’ BQSTUDIO illustrate what parameter-level work looks like: register access, data memory configuration, calibration, learning cycles, and production file generation. It is thorough work, but it is configuration, not firmware development.

Level 2: Protocol and Communication Customization

The supplier modifies or selects how the BMS communicates with external devices. This includes changing CAN message IDs, RS485/Modbus register maps, selecting inverter-specific protocols (Pylontech, Victron, Growatt, PACE), adjusting SMBus/SBS data fields, or modifying charger enable logic.

This level is the minimum for most ESS, e-bike, robotics, medical, industrial, and smart-battery applications. If your battery needs to talk to an inverter, controller, or display, you probably need at least this level.

Level 3: True Firmware Development

The supplier writes or modifies embedded firmware at the code level. This covers custom state machines, proprietary SOC/SOH algorithm tuning, fault logic, contactor control, secure bootloader design, OTA update capability, custom diagnostics, hardware abstraction for a new BMS PCB, and formal software release management.

Open-source BMS projects show what real firmware scope looks like. The Libre Solar BMS firmware, built on Zephyr RTOS, includes pack current/voltage measurement, single-cell monitoring, balancing control, SOC calculation, safety features, and CAN/serial communication.

Most commercial battery buyers don’t need source-code-level development. They need documented, validated BMS behavior that matches their product and host system. Define which level you need before contacting suppliers.

When Do You Need a Manufacturer With Custom BMS Firmware Capability?

Not every battery project requires firmware work. Here are the situations where it matters.

ESS inverter integration. A 48V or 51.2V rack battery for solar storage typically needs to report SOC, voltage, current, temperature, fault states, and charge/discharge limits over CAN or RS485 using a protocol the inverter recognizes. If the BMS can’t speak the right protocol, the battery may charge and discharge but won’t integrate properly. For projects involving LiFePO4 battery packs, this is one of the most common firmware-related requirements.

E-bike and e-scooter batteries. The BMS must match the controller, display, and charger. Discharge current limits, low-voltage cutoff behavior, and communication with the controller all depend on firmware or parameter settings. Some e-bike battery projects also require specific charging profiles or Bluetooth app support.

Laptop and portable smart batteries. These often need SMBus or SBS (Smart Battery System) behavior. The SBS Forum maintains specifications for smart battery data, chargers, selectors, and system managers that define how a battery communicates with a host device over SMBus.

Robotics, AGV, and industrial batteries. These typically need CAN bus data reporting and fault handling. Not just “CAN supported" but specific message formats, baud rates, and data maps.

Medical and safety-critical devices. These need conservative thresholds, traceable firmware versions, and sometimes cold-temperature charge blocking, self-heating logic, or redundant protection paths.

Any application requiring accurate SOC/SOH reporting, fault history logging, or charger handshake behavior. If your product shows a battery percentage, responds to faults, or negotiates with a charger, the BMS firmware is involved.

Which Type of Supplier Should You Contact?

This is where most online advice falls short. “Find a good manufacturer" is not helpful. The right supplier type depends on what you need.

Battery pack manufacturer with in-house BMS/PCBA is the most common fit for OEM buyers. Look for in-house SMT/PCBA capability, engineers who can discuss pack architecture and communication, sample testing, and the ability to maintain firmware version records by production lot. If you’re exploring OEM/ODM battery manufacturing, this is the supplier category to evaluate first.

BMS board manufacturers work well when you already have a pack builder and only need the electronics. Good signs include published BMS models by cell count and current rating, supported chemistries, protocol documentation, PC/mobile software, parameter write access, and firmware update tools. The risk is that they may not handle pack integration, thermal design, enclosure, or certification.

Embedded design houses serve high-complexity projects. They bring embedded C/C++ expertise, hardware bring-up, BMS IC experience, test harnesses, and formal version control. They rarely mass-produce battery packs or hold battery manufacturing certifications.

ESS/mobility ODMs are fast when existing protocol profiles cover your inverter or controller. If you need a proprietary protocol or unusual behavior, they may not be able to modify the underlying firmware.

How to Verify a Manufacturer Can Really Do Custom BMS Firmware

Saying “yes, we can do custom firmware" costs nothing. Proving it requires evidence. Here is a structured approach to verify capability.

Firmware Authority

Ask whether the supplier controls the firmware source code, only parameter files, or only third-party BMS settings.

Questions to ask:

• Is the BMS firmware developed in-house, by your BMS supplier, or by a third-party design house?
• Can you modify code, or only change parameters within an existing platform?
• Can you provide release notes and firmware revision identifiers?

Interface and Protocol Proof

Ask for exact communication details. Practitioners on the DIY Solar Forum explain that hardware protocol and software protocol are separate issues: CAN must connect to CAN and RS485 to RS485, but the software data format also has to match. Protocols like Pylontech, PACE, Growatt, and Victron are not automatically compatible with each other.

Do not ask only “Do you support CAN?" Ask: which CAN protocol, which message IDs, which baud rate, which data map, and can you provide a DBC file or register map? The same applies to RS485, Modbus, and SMBus.

Requirements Capture

A competent manufacturer should ask you for more than just voltage and capacity. Be prepared to provide cell chemistry, series/parallel configuration, continuous and peak current, charge current, operating temperature range, load profile, host communication requirements, required fault behavior, target certifications, and mechanical constraints.

If a supplier doesn’t ask these questions, they may not understand what custom BMS firmware entails.

Manufacturing Traceability

This is a blind spot in most sourcing conversations. Ask how the approved firmware becomes repeatable production. Is firmware version recorded per serial number or batch? Is the checksum verified at end-of-line testing? Are communication frames tested before shipment? Can parameters be locked after programming? Does the supplier keep golden samples and production files?

Understanding how a manufacturer handles quality control through production is just as important as evaluating their engineering capability.

Post-Sale Support

A LinkedIn engineer working on a 24S LiFePO4, 100Ah, 76V nominal BMS project reported real problems with a purchased BMS: zero-current readings sometimes appeared as 1A, SOC drifted, serial output contained garbage bytes, and support stopped responding after the issue was raised. This is not an isolated complaint.

Ask how long the manufacturer supports the firmware, what the bug-fix process looks like, whether they can reproduce old firmware builds, and what the RMA process is for firmware-related faults. Get these terms in writing before paying for tooling.

Validation Evidence

Ask for test evidence, not adjectives. Can they show sample test logs? Do they test OVP/UVP/OCP/OTP thresholds? Do they test communication under load? Intertek’s battery testing guidance explicitly ties BMS functional safety assessment to protection thresholds, fault detection, and relevant hardware/software functions.

Communication Protocols to Confirm Before Sampling

Communication failures are the most common surprise in custom BMS projects. Here is what to verify.

CAN bus is not a single protocol. CAN is a physical and data-link layer. On top of it, you might need CANopen (with SDO, PDO, NMT, and error-control mechanisms as defined by CAN in Automation), J1939, a proprietary inverter protocol, or raw CAN frames. Specifying “CAN" without defining the application-layer protocol is like saying “we need internet" without specifying HTTP, MQTT, or FTP.

RS485 is a physical layer. The software protocol on top, whether Modbus RTU, a proprietary register map, or an inverter-specific format, determines whether the battery and host device actually understand each other.

SMBus/SBS is common in laptop and portable battery applications. The data fields, charge/discharge behavior, and system manager interactions are defined by SBS specifications.

Bluetooth and UART are typically used for diagnostics, monitoring apps, or mobile configuration. If your product includes a customer-facing app, the BMS firmware needs to support the right data output format.

For every interface, ask for a protocol document, sample data frames, and a compatibility test with your specific host device before approving samples for production.

Compliance and Safety Questions to Ask

BMS firmware is not cosmetic. It is safety-critical.

In 2024, Mercedes-Benz recalled 15,351 model-year 2023 to 2025 EQE and EQS vehicles because BMS monitoring software might not meet production specifications, potentially causing loss of propulsion without warning. A CPSC report covering 2017 through 2024 documented 310 e-bike fatalities, including 19 associated with lithium-ion battery-related fire incidents.

These numbers don’t mean custom firmware causes fires. They mean that battery protection decisions, many of which live in firmware, have real consequences.

Firmware changes can affect certification status. Certifications and test reports are product-specific and configuration-specific. PHMSA requires lithium batteries to pass UN38.3 design tests for transport. Standards like UL 1973, UL 9540, and IEC 62133-2 evaluate protective functions, not just cell chemistry.

Ask these questions:

• Does this firmware change affect existing UN38.3, IEC 62133, UL 1973, UL 9540, CE, or RoHS documentation?
• Which exact model, SKU, and firmware revision is covered by each test report?
• Who pays for retesting if firmware changes after sample approval?

For more detail on transport compliance, the guide on UN38.3 battery requirements covers what documentation buyers need. You can also review Wintonic’s certifications and compliance documentation for applicable product lines.

Red Flags When Sourcing Custom BMS Firmware

These warning signs should make you pause or walk away.

1. Supplier says “yes, custom firmware" but only offers logo, label, or connector changes.
2. Supplier cannot name supported communication protocols.
3. Supplier says “CAN supported" but cannot provide message IDs, baud rate, or data map.
4. Supplier cannot say whether firmware is in-house or third-party.
5. No firmware version number appears on the sample report.
6. No way to recover from a failed firmware update. One Endless Sphere user described updating a smart BMS firmware file that restored UART but disabled Bluetooth entirely, and the seller could not provide the correct firmware.
7. No test report for OVP, UVP, OCP, or OTP behavior.
8. No record of which firmware version shipped in which production batch.
9. No engineering contact. All answers come through sales.
10. Supplier refuses to document settings before production.
11. Firmware updates erase parameters with no backup plan.
12. Certifications are shown for a different model, chemistry, or configuration.
13. The quote looks cheap but excludes protocol development, test fixtures, certification support, and post-sale debugging. A LinkedIn practitioner argues that a low-cost BMS can hide costs in inverter integration, SOC accuracy, firmware customization, communication support, and long-term software maintenance.

The biggest red flag of all: a supplier saying “yes, custom BMS firmware" but being unable to produce a firmware version, protocol document, parameter sheet, validation plan, or engineering contact.

RFQ Checklist for Custom BMS Firmware Projects

When you find a manufacturer that can do custom BMS firmware, submit an RFQ with these details so the engineering team can give a real answer instead of a vague “yes."

Technical Inputs

• Application (ESS, e-bike, robotics, UPS, medical, industrial, etc.)
• Chemistry (NMC, NCA, LFP, LTO, Li-polymer)
• Cell format and preferred cell model
• Series/parallel configuration
• Nominal and maximum voltage
• Capacity (Ah)
• Continuous discharge current
• Peak discharge current and duration
• Charge current and charger model or profile
• Load profile (constant, pulsed, regenerative)
• Operating temperature range
• Enclosure constraints, connectors, IP rating
• Communication interface (CAN, RS485, UART, SMBus, I2C, Bluetooth)
• Communication protocol or host device model
• Required telemetry (per-cell voltage, pack voltage, current, temperatures, SOC, SOH, fault codes, cycle count)
• Fault behavior requirements
• Sleep/wake and low-power requirements
• Data logging requirements
• Firmware update requirements (wired, OTA, factory-only)
• Target certifications and markets
• Expected annual volume and prototype quantity

Firmware-Specific Questions

• Is the BMS firmware developed in-house?
• Can you modify source code, or only configure parameters?
• Which BMS IC and MCU platform do you use?
• Can you support our protocol? What documentation do you need from us?
• Can you provide a CAN DBC, RS485 register map, or SMBus command list?
• Can you provide firmware release notes?
• Can you lock the approved firmware for production?
• How is firmware version tracked per pack?
• Can firmware be updated in the field?
• What is the rollback and recovery method?
• What test evidence do you provide with samples?
• Does this firmware revision affect certification or transport documents?

Ownership and IP Questions

• Do we receive source code, binaries only, or parameter files only?
• Who owns custom protocol changes?
• Can we get documentation under NDA?
• Can firmware be restored if a pack is bricked?
• What happens if the BMS IC or MCU becomes unavailable?
• Do you provide long-term firmware support after mass production?

How to Submit Your Custom BMS Requirements for Review

For projects that need custom lithium packs with specific BMS behavior, communication protocols, or protection requirements, include the firmware and protocol details from the checklist above in your inquiry. The more specific you are about chemistry, pack configuration, host device, communication interface, and target certifications, the faster an engineering team can confirm what is feasible.

Request a quote from Wintonic with your pack voltage, chemistry, capacity, current limits, charger or inverter model, communication protocol, target market, certification needs, and expected order volume.

FAQ

Can any lithium battery manufacturer do custom BMS firmware?

No. Many battery manufacturers assemble packs and install a standard BMS, but they don’t control the firmware. Some can only change configurable parameters. To find a manufacturer that can do custom BMS firmware, look for in-house BMS/PCBA engineering or a supplier with a documented BMS firmware partner.

Is custom BMS firmware the same as a smart BMS?

No. A smart BMS supports communication, monitoring, and settings, but that doesn’t mean the supplier can modify firmware code. A smart BMS may only allow parameter programming within a fixed platform.

What is the single most important question to ask a supplier about custom BMS firmware?

Ask: “Do you develop the BMS firmware in-house, or are you configuring a third-party BMS?" Then follow up by asking what deliverables they can provide: protocol document, firmware version identifier, parameter file, test report, and update/recovery process.

Do I need custom firmware for an inverter-compatible battery?

It depends. If the inverter supports the battery’s existing protocol, you may only need parameter configuration. If the inverter requires a different CAN or RS485 protocol, custom data map, or specific handshake behavior, you need at least protocol customization and possibly firmware modification.

Can firmware changes affect my battery’s certification?

Yes. If firmware changes affect protection thresholds, fault detection, charging limits, or system-level safety behavior, the existing test reports may no longer apply to the modified configuration. Always ask which reports cover the exact model, firmware revision, and chemistry you plan to ship.

Should I ask for source code from my BMS firmware supplier?

For most OEM battery buyers, source code transfer is uncommon and usually unnecessary. More practical deliverables include firmware version IDs, release notes, protocol documentation, binary/update files (if field updates are needed), recovery procedures, and long-term support terms. If source code ownership is critical, discuss it before design begins, because it will affect pricing and supplier willingness.

Can a custom BMS firmware manufacturer also handle cell sourcing and pack assembly?

Some can. Battery pack manufacturers with in-house BMS/PCBA engineering and cell production or sourcing can handle the full scope from cells to firmware to finished pack. Others, like standalone BMS board makers or embedded design houses, handle only the electronics or software. Match the supplier type to your project scope.

What is the difference between a BMS and a PCM?

A PCM (protection circuit module) is typically a simpler board that handles basic over-voltage, under-voltage, over-current, and short-circuit protection. A BMS, especially a “smart BMS," adds communication, monitoring, diagnostics, SOC/SOH reporting, balancing, and sometimes firmware update capability. Custom firmware work applies to BMS-level systems, not basic PCMs.