The day to day activities for a Business Analyst would vary depending on each organization's structure, process, methods, team size, etc. 

Some of the things you might be expected to perform could include:

• Performing systems analysis of the interfaces of the third party systems you are supposed to integrate with,
• Conduct requirement elicitation sessions or JAD sessions with the billing department to understand the detailed requirements of the reports and driver patterns they want to see,
• Interface with the technical team supporting the billing system to understand the existing structure and features of that system,
• Hold requirement workshops with the project stakeholders to understand the high-level vision and goal of the project,
• Manage the requirements for the project: elicit, document, analyze, confirm, and refine.
• Create functional specifications for the desired changes.
• etc.

- Adrian