The engineering decision
Build a requirement with measurable acceptance criteria and explicit open decisions. Use it to agree the next engineering review and its required evidence.
Have these inputs ready
- Application and mission
- Voltage/current/time profile
- Mechanical and environmental constraints
- Markets, validation, volume and lifecycle
Each requirement must reach a verification method
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Specify the equipment boundary first
Start with the application, intended use and operating states. Name the equipment interface where voltage and current limits apply. A nominal 24 V or 48 V label leaves maximum charge voltage, minimum loaded voltage and transient tolerance unresolved.
Describe available volume, mass, mounting, connector orientation, service access and environmental conditions. Include charging, communications and safe-state behavior so electrical choices can be assessed within the physical product.
For an existing design, attach controlled drawings, BOM, firmware/configuration and validation reports with a change list. For a new design, state the known constraints and which architecture decisions remain open.
| Area | Required inputs | Verification output |
|---|---|---|
| Mission | States, durations, payload and route | Representative duty-cycle test |
| Electrical | Full voltage window, peaks, duration and repetition | Loaded voltage and thermal acceptance |
| Mechanical | Envelope, mass, mounting and interfaces | Drawing review and integration fit |
| Environment | Temperature, ingress, vibration and storage | Application-specific validation matrix |
| Charging / controls | Source, recharge window, protocol and fault response | Charge/transition and communication tests |
| Markets | Destination, transport mode and intended use | Applicability matrix |
| Production / lifecycle | Quantities, records, service and change policy | Release and repeat-supply plan |
Resolve an incomplete “48 V, 20 Ah” request
Consider a hypothetical robot brief containing only 48 V nominal and 20 Ah. Suppose the later mission review requires 900 Wh at the battery terminals, with only 80% of validated usable energy allocated to the mission. The usable-energy target becomes 1,125 Wh. The nominal 960 Wh arithmetic from the original label cannot demonstrate that requirement.
If the equipment also needs 2.4 kW at a 40 V minimum input, the pack must support a 60 A event with defined duration and repetition. The series/parallel architecture, protection settings and enclosure cannot be finalized until those conditions and the charge-voltage ceiling are known.
Turn missing information into an engineering task
| Missing input | Unresolved decision | Next action |
|---|---|---|
| Peak duration | Switch and cell pulse/thermal requirement | Capture the operating event |
| Equipment minimum voltage | Sag margin and usable energy | Obtain controller limits; verify at interface |
| Charger behavior | Power path and recharge time | Review source/charger data and transitions |
| Destination markets | Compliance scope | Complete application/market matrix |
| Environmental limits | Enclosure and validation conditions | Define service and storage envelope |
| Production records | Acceptance and containment coverage | Agree the batch data schema |
Define the review output before requesting it
A first review should return a requirement baseline, unresolved questions, architecture options and the evidence needed to compare them. A feasibility estimate can use explicit assumptions; those assumptions need owners and closure criteria before design release.
Link every critical requirement to a verification method and responsible party. A requirement such as “high current” is not testable. “Maintain at least the agreed terminal voltage during the recorded peak sequence at the specified service conditions” can be translated into a test.
Agree how changes are handled after approval. A different cell, charger, connector, BMS configuration or enclosure can affect validation and production evidence. Keep lifecycle replacements and record retention inside the same controlled process.
Measurement & validation procedure
| Test / review | Record | Acceptance condition |
|---|---|---|
| Review completeness | Known values and open-decision register | Every critical unknown has an owner and resolution method |
| Link requirements to validation | Requirement ID, method, condition and acceptance | Critical functions have measurable criteria |
| Prepare the engineering handoff | Brief, supporting files and requested review output | Next decision and evidence package are explicit |
Continue this engineering task
Related engineering guidance
Prepare the evidence for review
- Mission and current-time profile
- Equipment/charger data and drawings
- Markets, environment and validation targets
- Quantity, timing and production-record expectations
Technical sources & claim support
References support the stated engineering principles. Worked examples use their explicitly stated assumptions.
- Molicel INR-21700-P45B product data sheet, revision 1.2 ↗
Cell specifications; discharge-rate and temperature characteristics
Cell-specific capacity, impedance and rate/temperature data; worked examples state their own input values.
- Texas Instruments BQ76952 data sheet, SLUSE13B ↗
Sections 7 and 10–12: electrical characteristics, measurement, protection and FET control
Example of a monitor/protector architecture; capabilities depend on the selected IC and complete circuit.
- Texas Instruments BQ25798 data sheet ↗
Power-path management; battery supplement mode; charge termination
Low-voltage power-path example covering load sharing, charge termination and battery supplement mode; apply the device voltage and current limits.
- IEC 62619:2022 ↗
Official scope: industrial secondary lithium cells and batteries
Industrial-cell and battery safety scope; develop the conformity test plan from the full standard and applicable edition.
- ISO 9001:2026 — Quality management systems: requirements and official publication status ↗
Quality management systems; consistency of products and services
Quality-system context for documented information, process control and traceable production records.
Key claims and evidence
| Claim | Basis | Reference |
|---|---|---|
| Nominal Ah alone leaves system limits unresolved | inference | Molicel INR-21700-P45B product data sheet, revision 1.2; Texas Instruments BQ76952 data sheet, SLUSE13B |
| Illustrative energy allocation requires 1125 Wh usable | calculation | calculation |
| Requirement-to-verification mapping is a proposed workflow | workflow | engineering workflow |