In custom battery pack projects, clients need to provide key information to ensure the battery meets their requirements. This includes details about the device type, usage, operating parameters, and space constraints. Information about the operating environment, such as temperature, humidity, and potential exposure to vibrations or shocks, is crucial. Clients should also specify performance needs, like battery life, charging requirements, and safety features. Additionally, any special requirements related to cost, project timeline, branding, or design should be communicated to ensure the battery pack is tailored to their specific needs.