Usable capacity differs from total capacity: Lithium batteries provide 90-95% usable capacity while lead-acid only offers 50%. Factor in 10-15% efficiency losses and plan for 20% capacity degradation over 10 years when sizing your system. Oversized and budget sit in idle capacity. This UL9540A-compliant battery solution reduces battery footprint and weight by up to 70%, allowing more effective use. The exact math for sizing your battery system is based on your daily power usage and the battery type. Based on usage of 10kWh per day, here are some examples: 10kWh x 2 (for 50% depth of discharge) x 1.