The project charter does not replace a project management plan. In fact, project initiation is the prerequisite to project planning: You can’t plan a project until the project exists. Therefore, I don’t expect the charter to include a detailed task list, a complete deliverable list, resource allocations, project tracking or control procedures, and so forth.
Nor is the charter a requirements specification. Let me qualify that slightly. I think in terms of three levels of software requirements (Wiegers 2003):
Business requirements describe why we are undertaking the project, typically by stating business objectives. This kind of information could indeed be presented in the charter. Alternatively, a vision and scope document could serve as a container for the business requirements if a higher-level project charter is created as a separate document.
User requirements describe what the user will be able to do with the product. These are typically stated in the form of use cases or event-response tables. User requirements could also include nonfunctional requirements, including the users’ performance and quality expectations.
Functional requirements describe what the developers build; the behaviors the system will exhibit under specified conditions.
The project charter could contain or point to some business requirements information, but it definitely should not contain user requirements, functionality descriptions, quality and performance requirements, business rules, interface specifications, data definitions, or other types of requirements information.
I once encountered an organization that created just a single document for each project, which they called "The Specification." Their specification document was a melange of project plans, requirements, design specifications, and everything else under the sun that somehow related to that project. This made it difficult to manage those diverse kinds of information effectively. Creating a discrete project charter, project management plan, requirements specification, quality assurance plan, and configuration management plan is a good idea for every software project.