When evaluating rack batteries, prioritize LiFePO4 (Lithium Iron Phosphate) chemistry due to its superior thermal stability and cycle life. Key specs include nominal voltage (typically 48V or 51.2V), capacity (Ah), and energy density (kWh). Ensure the battery features a high-quality Integrated Battery Management System (BMS) that monitors cell balancing, over-charge, and over-discharge protection. For scalability, verify the maximum number of parallel connections supported to ensure the system can meet future power expansion needs.