Battery Bank Capacity Calculator
Calculate required usable and total battery capacity.
Battery Bank Capacity Calculator sizes your battery storage in kWh and Ah based on daily energy needs, autonomy days, system voltage, and depth of discharge. Getting the capacity right depends heavily on which battery chemistry you choose, because each type has a different usable percentage of its total rated capacity. Lithium Iron Phosphate (LiFePO4) batteries are the most popular choice for modern off-grid and solar systems. They can safely be discharged to 80-90% of their rated capacity on every cycle, giving you the most usable energy per kilogram. They also tolerate thousands of deep cycles (3,000-5,000+ at 80% DoD) and maintain a flat voltage curve, so appliances run consistently until the battery is nearly empty. Set Max DoD to 80-90% and efficiency to 95-98% for LiFePO4. Flooded Lead-Acid (FLA) batteries are the traditional budget option. They should only be discharged to about 50% of rated capacity to avoid accelerated degradation. That means a 200 Ah FLA bank only delivers roughly 100 Ah of usable energy. Cycle life at 50% DoD is typically 300-700 cycles. They also require regular topping-up with distilled water and good ventilation because they off-gas hydrogen during charging. Set Max DoD to 50% and efficiency to 80-85% for FLA. AGM (Absorbent Glass Mat) batteries are a sealed, maintenance-free variant of lead-acid. They handle vibration well and do not off-gas under normal conditions, making them suitable for RVs and marine installations. Usable depth of discharge is similar to FLA at around 50%, though some premium AGM models support up to 60%. Cycle life is comparable at 400-800 cycles. Set Max DoD to 50% and efficiency to 85-90% for AGM. Gel batteries are another sealed lead-acid variant that use a silica-based gel electrolyte. They perform better in high-temperature environments and are very resistant to deep discharge damage compared to FLA or AGM. Recommended DoD is 50-60%, with a cycle life of 500-1,000 cycles. Set Max DoD to 50-60% and efficiency to 85-90% for Gel. Lithium-Ion NMC (Nickel Manganese Cobalt) batteries, common in home storage products like the Tesla Powerwall, offer high energy density and round-trip efficiencies of 90-95%. Typical usable DoD is 80-90% with a cycle life of 2,000-4,000 cycles. They require a battery management system (BMS) and are more sensitive to high temperatures than LiFePO4. Set Max DoD to 80-90% and efficiency to 90-95% for NMC. Sodium-Ion batteries are an emerging chemistry that uses abundant, low-cost materials. Current usable DoD is around 80% with round-trip efficiency of 85-90%. Cycle life ranges from 2,000-4,000 cycles. They perform well in cold climates and have no thermal runaway risk. Set Max DoD to 80% and efficiency to 85-90% for Sodium-Ion. As a rule of thumb, always size your battery bank using the usable capacity (after DoD), not the nameplate rating. A 10 kWh lead-acid bank at 50% DoD gives you only 5 kWh of usable storage, while a 10 kWh LiFePO4 bank at 80% DoD gives you 8 kWh. This calculator accounts for both depth of discharge and round-trip efficiency so you can compare chemistries side by side.