Adds a battery product to a specific solar system design.

Business Context:
Battery storage systems are increasingly important components of solar installations,
providing energy storage, backup power, and grid services capabilities. This endpoint
allows partners to specify battery equipment for solar designs.

Battery Integration:

• Energy Storage: Store excess solar production for later use
• Backup Power: Provide power during grid outages
• Load Shifting: Use stored energy during peak rate periods
• Grid Services: Support grid stability and demand response

Optional Configuration:

• Monitoring Location: Physical location for monitoring equipment
• Monitoring ID: Identifier for monitoring system integration