The integration of Battery Management Systems (BMS) into battery systems within the European Union requires compliance with the CE marking framework, particularly under the Machinery Directive (2006/42/EC). This directive ensures that machinery, including BMS-integrated battery systems, meets essential health and safety requirements before being placed on the market. The process involves adherence to Electromagnetic Compatibility (EMC), Low Voltage Directive (LVD), and rigorous risk assessment procedures, followed by documentation and conformity assessment.

**EMC Directive (2014/30/EU)**
BMS-integrated battery systems must comply with the EMC Directive to ensure electromagnetic emissions do not interfere with other devices and that the system itself is immune to external disturbances. Key standards include EN 61000-6 series for industrial environments and EN 61326 for electrical equipment in laboratories. Testing covers conducted and radiated emissions, electrostatic discharge immunity, and fast transient burst immunity. Manufacturers must ensure that the BMS does not exceed emission limits and maintains functionality under electromagnetic disturbances typical of its operating environment.

**Low Voltage Directive (2014/35/EU)**
The LVD applies to BMS-integrated battery systems operating between 50V AC and 1000V AC or 75V DC and 1500V DC. Compliance ensures protection against electrical hazards such as short circuits, insulation failures, and overheating. Harmonized standards like EN 62133 for secondary cells and batteries, or EN 50604 for lithium-ion batteries in industrial applications, provide specific safety benchmarks. Key requirements include adequate insulation, protection against direct and indirect contact, and thermal stability under normal and fault conditions.

**Risk Assessment Under the Machinery Directive**
A systematic risk assessment is mandatory to identify and mitigate hazards associated with BMS-integrated battery systems. The process follows EN ISO 12100, which outlines principles for risk assessment and risk reduction. Hazards specific to battery systems include thermal runaway, electrical shock, mechanical failure, and chemical exposure. The assessment must evaluate:
- Potential ignition sources in high-energy battery systems.
- Failures in cell balancing leading to overcharging or over-discharging.
- Mechanical integrity under vibration or impact.
- Environmental conditions such as temperature extremes or humidity.

Risk reduction measures may include redundant safety circuits, fail-safe mechanisms in the BMS, and robust enclosure designs to contain thermal events.

**Technical Documentation and Conformity Assessment**
Manufacturers must compile a technical file containing:
- Detailed design and manufacturing drawings.
- List of applied harmonized standards.
- Risk assessment report.
- Test reports from accredited laboratories (EMC, LVD, safety).
- Instructions for installation, use, and maintenance.

For most BMS-integrated battery systems, self-certification (Module A) under the Machinery Directive is permissible if harmonized standards are fully applied. If standards are not fully applied or do not exist, a notified body must be involved for additional evaluation (Module B followed by Module C or D). The EU Declaration of Conformity must accompany the product, stating compliance with all applicable directives.

**CE Marking Process**
The CE mark is affixed only after full compliance is confirmed. Steps include:
1. Identify applicable directives (Machinery, EMC, LVD).
2. Conduct risk assessment and implement mitigation measures.
3. Perform testing per harmonized standards.
4. Compile technical documentation.
5. Draft and sign the EU Declaration of Conformity.
6. Affix the CE mark visibly on the product or its data plate.

**Ongoing Compliance and Market Surveillance**
Post-market surveillance is critical to ensure continued compliance. Manufacturers must monitor field performance, report incidents to authorities, and initiate recalls if non-conformities are found. The EU market surveillance framework (Regulation (EU) 2019/1020) empowers authorities to conduct checks and demand corrective actions for non-compliant products.

In summary, CE marking for BMS-integrated battery systems under the EU Machinery Directive requires a multi-faceted approach covering EMC, electrical safety, and risk management. Proper documentation, adherence to harmonized standards, and a structured conformity assessment route are essential for legal market access in the EU. Compliance not only ensures regulatory approval but also enhances system reliability and safety for end-users.