Enter your Battery Capacity, Battery Voltage, Battery Type, and Number of Batteries to find your Total Capacity, Total Energy Storage, and Usable Capacity — add an optional Load Power and Minimum Remaining Charge to also get your Estimated Runtime.
Total Capacity
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Total Energy Storage
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Capacity in mAh
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Usable Capacity
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Estimated Runtime
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Amp hours (Ah) measure how much electric charge a battery can deliver over time. One amp hour means the battery can provide 1 amp of current for 1 hour, or 2 amps for 30 minutes, etc.
To convert Ah to Wh: multiply by voltage (Ah × V = Wh). To convert Ah to mAh: multiply by 1000 (Ah × 1000 = mAh). To convert Wh to Ah: divide by voltage (Wh ÷ V = Ah).
Lead acid batteries should not be discharged below 50% to maintain lifespan, while lithium batteries can safely discharge to 20%. This means lithium batteries have more usable capacity.
Divide the usable battery capacity (Ah) by your device's current draw (A). For example, a 100Ah battery with 80Ah usable capacity powering a 5A load will run for 16 hours (80 ÷ 5 = 16).
Temperature, age, discharge rate, and charging cycles all affect real-world capacity. Cold temperatures reduce capacity, while high discharge rates (C-rate) can also decrease available energy.
Calculate your daily energy needs in kWh, then divide by your chosen battery capacity. Account for days of autonomy (backup days) and depth of discharge limits for your battery type.
C-rate is the discharge rate relative to battery capacity. 1C means discharging the full capacity in 1 hour. Higher C-rates (faster discharge) typically reduce the actual available capacity.