Why Detailed Circuit Schematics Are Not Provided Before Battery Prototyping?

This is an excellent question frequently asked by clients new to custom battery pack development. In short, suppliers typically cannot provide 

a "one-to-one, production-ready" detailed circuit schematic draft before prototyping. This is not a lapse in service but is dictated by technical 

logic, commercial practices, and standard development workflows.

The core reasons are outlined below:

1. Technical Logic: Battery Design is "Parameter-Driven," Not "Drawing-First"

A battery pack is a highly customized system-integrated product. Its design originates from client specifications, not from creating a circuit 

diagram in a vacuum.

Driven by Requirements, Not a Sketch: A reliable battery design starts with a clear Product Requirement Specification (PRS), detailing:

Electrical Parameters: Voltage, capacity, discharge rate (peak/continuous), charge current, cycle life, etc.

Mechanical Parameters: Dimensions, weight constraints, mounting method, enclosure material (IP rating), etc.

Protection & Functional Requirements: Over-charge/discharge/current, short-circuit, and temperature protection; communication protocols 

(UART, I2C, CAN, SMBus); display method; cell balancing, etc.

Compliance & Environmental Needs: Target certifications (CE, UL, UN38.3), operating temperature range, vibration requirements, etc.

The Schematic is an "Output," Not an "Input": The circuit schematic is a technical deliverable created by engineers only after finalizing all 

key details: cell selection (series/parallel configuration), BMS IC selection, charging strategy, load interfaces, etc. Without these foundational 

parameters, a drawing is meaningless. A supplier can provide a generic or reference block diagram to illustrate the design concept, but a 

precise schematic is produced during the detailed design phase.

2. Commercial & Intellectual Property Protection

Supplier's Core IP: For a professional battery pack manufacturer, their BMS circuit design—especially the protection algorithms, balancing 

strategies, and firmware code—constitutes core intellectual property and competitive advantage. Providing detailed schematics before formal 

engagement (e.g., signed contract, paid prototype fee) poses a risk of technology leakage.

Preventing Design "Farming": If a supplier freely provides a complete design draft, a client could potentially use it to solicit lower bids from 

other manufacturers. This undermines the supplier's upfront technical consultation efforts. The prototype fee (which typically includes a design 

component) establishes mutual commitment and trust.

3. Standardized Development Process

A formal battery prototyping process typically follows these stages, with the schematic appearing mid-to-late:

1.Requirement Gathering & Confirmation: Client provides detailed specs → Supplier evaluates feasibility and provides feedback.

2.Solution Design & Quotation: Supplier creates a Technical Proposal (including cell recommendations, BMS functional block diagram, 

mechanical concept, estimated parameters) and a Commercial Quotation. The circuit framework and functionality can be discussed and 

agreed upon here, but no detailed drawings are provided.

3.Contract & Prototype Fee Payment: Both parties agree on the solution and price, formally initiating the project.

4.Detailed Design Phase: After payment, the supplier's engineers begin:

Completing the detailed circuit schematic.

Performing PCB layout and routing.

Designing mechanical part drawings.

Developing/configuring BMS firmware.

5.Prototyping & Testing: Building prototype units and conducting comprehensive in-house tests.

6.Delivery & Validation: Delivering tested, qualified samples to the client for verification.

The schematic is a deliverable within the "Detailed Design Phase," which occurs after the project is officially launched and fees are paid.

As a Client, What Can You Do?

1.Provide the Most Detailed Requirement Document Possible: Clearer requirements lead to a more accurate supplier proposal and efficient 

communication.

2.Request a "Technical Proposal" or "Design Block Diagram": During the quotation stage, you can ask for a non-confidential, high-level system 

block diagram. This should illustrate the power path, protection logic, communication interfaces, etc., and is sufficient to evaluate the design 

approach.

3.Clarify Key Design Points: Ask specific questions like: "What BMS controller IC architecture will be used (e.g., TI, NXP, proprietary)?" "Is 

over-current protection implemented via hardware comparator or software?" "Does it support cell balancing? Active or passive?" These 

questions better assess a supplier's technical capability than simply requesting drawings.

4.Understand the Purpose of the Prototype Fee: This fee covers not only material and machining costs but also the preliminary design labor 

and engineering effort. Paying it is a necessary step to receive customized design outputs, including schematics and physical samples.

Summary

The inability to provide a customized schematic draft before prototyping is a common, reasonable, and professional industry practice. The 

underlying rationale is:

Technically: Design must start from parameters; the schematic is the result of that process.

Commercially: It protects intellectual property and ensures serious collaboration.

Procedurally: It follows a structured R&D process where the schematic is a deliverable after project kickoff.

The best way to evaluate a supplier is through in-depth requirements discussion and careful review of their technical proposal. Once the 

project begins, you will receive complete technical documentation, including the production-ready circuit schematic.