Requirements

How to Write a Battery System Requirements Specification

A battery system requirements checklist ensures you capture all critical specifications for custom lithium-ion battery systems, including UAV battery system applications, from electrical performance to safety standards. Structured approach to capturing electrical, physical, environmental, safety, and lifecycle requirements with traceability and testability.

12 min read•Intermediate•Last updated: 2026-01-15

Goal Statement

You will end with a complete battery system requirements specification document that:

  • Captures electrical, physical, environmental, safety, and lifecycle requirements
  • Uses testable, traceable, and unambiguous requirement statements
  • Defines verification approach for each requirement category
  • Establishes clear acceptance criteria boundaries (even if specific values TBD)
  • Enables engineering vendors to provide accurate proposals and design solutions

Prerequisites & Assumptions for UAV Battery System Requirements

Prerequisites

  • Understanding of platform mission profile and operational scenarios
  • Knowledge of power requirements (continuous and peak)
  • Access to platform interface specifications (mechanical, electrical, thermal)
  • Awareness of applicable safety standards and regulatory requirements

Constraints & Assumptions

  • Assumes: Requirements author has access to stakeholders for clarification
  • Assumes: Basic understanding of battery system architecture (voltage, capacity, BMS)
  • Constraint: This process captures requirements, not design solutions
  • Constraint: Specific test procedures and pass/fail values will be coordinated with vendor

Step-by-Step Procedure

1

Define System-Level Objectives

Document mission profile, platform integration constraints, and success criteria. Capture operational scenarios, duty cycles, and performance targets without specifying implementation details. Example objectives: "Provide 10kWh usable energy for 2-hour flight mission" rather than "Use 200 cells in 50S4P configuration."

2

Specify Electrical Requirements

Define nominal voltage, voltage range (Vmin–Vmax), energy requirement (kWh usable), continuous power (kW), peak power (kW with duration), and charge rate (if applicable). Include load profile characteristics: constant power, pulsed, regenerative. Specify bus capacitance if known or state as interface requirement.

3

Define Physical Requirements

Specify maximum envelope dimensions (L × W × H), maximum mass, mounting interface (hole patterns, fastener specs), center of gravity constraints (if critical), and connector locations. Use drawings or CAD references for complex geometries. State tolerance requirements for critical dimensions.

4

Capture Environmental Requirements

Define operating temperature range, storage temperature range, altitude range (pressure), humidity exposure, vibration profile (frequency range and amplitude or reference standard like MIL-STD-810 or DO-160), shock levels, and ingress protection rating (IP rating). Reference test standards where applicable rather than inventing test procedures.

5

Specify Safety and Fault Tolerance Requirements

Define safety interlock requirements (HVIL, E-stop response time), fault detection requirements (overvoltage, undervoltage, overcurrent, overtemperature thresholds as percentages or "to be coordinated"), isolation resistance requirements, and fail-safe behavior. Reference applicable safety standards (IEC 62619, UL 2271, SAE J2464) as baseline.

6

Define Interface Requirements

Specify electrical interfaces (connector type, pin assignments, mating connector if known), mechanical interfaces (mounting pattern, thermal interface for conduction cooling), thermal interfaces (coolant type, flow rate range, inlet/outlet locations for liquid cooling), and communication interfaces (CAN, Modbus, update rates, message structure or reference to ICD).

7

Specify Performance and Lifecycle Requirements

Define cycle life requirement (number of cycles to X% capacity retention), calendar life (years to Y% retention), efficiency target (round-trip or discharge only), response time for power steps, state estimation accuracy requirements (SOC, SOH), and end-of-life criteria.

8

Define Verification Requirements

State what verification approach is required: analysis, inspection, demonstration, or test. Identify critical requirements needing formal test validation. Specify test environment requirements (thermal chamber, vibration table, altitude chamber). Define acceptance criteria categories (pass/fail thresholds to be coordinated with vendor).

9

Establish Traceability Structure

Assign unique requirement IDs using structured format (e.g., BATT-ELEC-001, BATT-MECH-005). Create traceability matrix linking requirements to verification methods. Tag requirements as mandatory, performance, or desirable. Identify derived requirements that will emerge during design.

10

Document Assumptions and Constraints

Explicitly state assumptions: ambient conditions for performance specs, duty cycle definitions, cooling system availability, platform interfaces. Document constraints: budget, schedule, regulatory, export control. Identify requirements dependent on external interfaces or platform characteristics.

11

Define Documentation Deliverables

Specify required deliverables: design documentation (drawings, schematics, BOM), test data (qualification test reports, acceptance test data), certifications (if applicable and achievable), user documentation (integration manual, safety warnings), and ICD (Interface Control Document for electrical, mechanical, thermal, communication interfaces).

12

Review and Validate Completeness

Conduct requirement review with stakeholders: systems engineers, integration engineers, test engineers. Verify requirements are unambiguous, testable, and traceable. Check for conflicts or gaps. Ensure requirements focus on outcomes rather than implementation. Iterate based on feedback before issuing as baseline.

Common Pitfalls & Troubleshooting

Pitfall: Over-Specifying Implementation Details

Problem: Requirements specify cell chemistry, topology (50S4P), or BMS architecture rather than performance outcomes.

Solution: Focus on what the system must achieve (energy, power, voltage range, life) and let the vendor optimize implementation. Specify outcomes, not solutions.

Pitfall: Ambiguous or Untestable Requirements

Problem: Requirements use vague language like "battery shall be lightweight" or "system shall be reliable."

Solution: Use quantitative metrics with clear bounds. "Battery mass shall not exceed 25kg" or "System shall achieve 2000 cycles to 80% capacity retention at 1C discharge."

Pitfall: Ignoring Tradeoff Dependencies

Problem: Requirements demand maximum energy, minimum weight, lowest cost, and longest life simultaneously without acknowledging tradeoffs.

Solution: Prioritize requirements (mandatory vs desirable). Engage vendor early to understand tradeoff space. Be prepared to adjust secondary requirements based on primary constraints.

Pitfall: Missing Interface Requirements

Problem: Electrical performance specified but connector type, communication protocol, or thermal interface left undefined until late in design.

Solution: Document all interfaces early: electrical (connector, signals), mechanical (mounting, mating surfaces), thermal (coolant, conduction interface), communication (CAN message structure, update rates).

Pitfall: Invented Environmental Test Values

Problem: Specifying "5G vibration" or "50,000 ft altitude" without understanding actual platform exposure or test implications.

Solution: Reference platform environmental specifications. If unknown, state "to match platform exposure per [reference document]" or "to be coordinated based on qualification test approach."

Decision Framework: When to Use ForgeConfigurator vs Request Consultation

Use ForgeConfigurator When:

  • Exploring MonoLith configurations by voltage/energy range
  • Requirements are within standard MonoLith voltage bands (24V–800V nominal)
  • Scoping feasibility before detailed requirements capture
Explore Configurations

Request Consultation When:

  • Requirements include custom voltage, non-standard energy capacity, or unique interfaces
  • Need guidance on requirements capture, tradeoff analysis, or validation approach
  • Project requires detailed ICD development or interface coordination
Contact Engineering

Inputs Checklist: Required for Vendor Engagement

Nominal voltage and voltage range (Vmin–Vmax)
Energy requirement (kWh usable)
Continuous and peak power (kW, duration)
Operating temperature range
Maximum dimensions (L × W × H)
Maximum mass
Cooling method (air, liquid, conduction)
Communication protocol (CAN, Modbus, etc.)
Safety standards or test requirements
Cycle life / calendar life expectations
Development timeline
Quantity expectations (prototype, production)

Verification & Acceptance Criteria

Requirements specification is complete when it satisfies these acceptance categories:

Completeness

All requirement categories addressed: electrical, physical, environmental, safety, interfaces, lifecycle, verification, documentation.

Testability

Each requirement can be verified through analysis, inspection, demonstration, or test. Acceptance criteria are quantitative or have clear pass/fail definitions.

Traceability

Requirements have unique IDs. Traceability matrix links requirements to verification methods. Derived requirements are flagged.

Stakeholder Approval

Systems engineers, integration engineers, and test engineers have reviewed and approved requirements baseline. Conflicts and gaps have been resolved.

Vendor Usability

Requirements document enables engineering vendors to provide accurate proposals, assess feasibility, and begin preliminary design without excessive clarification requests.

Related Resources

Battery Requirements Definition

Framework for electrical, physical, environmental, and safety requirements with testability guidance.

Documentation Deliverables

Technical documentation expectations for battery projects including ICDs and test plans.

Article Information

Reviewed By

Justin Dunn

Founder & CEO

Last Updated

January 15, 2026

Sources & Standards Referenced

No external sources listed. This content is based on engineering principles and EVolve's design experience.

Sources & Standards Referenced

  • • IEC 62619: Secondary cells and batteries containing alkaline or other non-acid electrolytes. Safety requirements for secondary lithium cells and batteries, for use in industrial applications
  • • UL 2271: Standard for Safety for Batteries for Use in Light Electric Vehicle (LEV) Applications
  • • SAE J2464: Electric and Hybrid Electric Vehicle Rechargeable Energy Storage System (RESS) Safety and Abuse Testing
  • • MIL-STD-810: Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests
  • • DO-160: Environmental Conditions and Test Procedures for Airborne Equipment

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