Battery Capacity Calculator

Enter your battery capacity (in mAh, Ah, Wh, or kWh), battery voltage, and load current to calculate battery life, energy stored, and C-rate. You can also input the number of batteries and battery type for a full bank analysis. Results include estimated runtime, total watt-hours, and charge capacity in multiple units.

Enter the rated capacity of a single battery.

V

Nominal voltage of a single battery.

Total batteries wired together in the bank.

Battery chemistry affects usable depth of discharge.

Average current your device draws from the battery.

Results

Estimated Battery Life

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Battery Life (Days)

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Total Bank Capacity (Ah)

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Total Energy Stored (Wh)

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Usable Energy (Wh)

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C-Rate

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Depth of Discharge (DoD)

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Usable vs. Reserved Energy

Frequently Asked Questions

What are battery amp hours (Ah)?

Amp-hours (Ah) measure the electric charge a battery can deliver over time. A 100 Ah battery can supply 1 amp for 100 hours, or 10 amps for 10 hours. It tells you how much total current the battery can provide before it is fully discharged.

How do I calculate battery life from amp hours?

Battery life (hours) = Battery Capacity (Ah) ÷ Load Current (A). For example, a 100 Ah battery powering a 5 A device would last approximately 20 hours. This calculator applies a depth-of-discharge factor based on battery chemistry to give a more realistic estimate.

What is the capacity of a battery in watt-hours?

Watt-hours (Wh) = Voltage (V) × Capacity (Ah). A 12 V, 100 Ah battery stores 1,200 Wh (1.2 kWh) of energy. Watt-hours are useful when comparing batteries of different voltages or calculating energy costs.

What is the C-rate of a battery?

The C-rate describes how quickly a battery is charged or discharged relative to its total capacity. A C-rate of 1C means the battery is fully discharged in 1 hour. A rate of 0.5C discharges it in 2 hours. Higher C-rates can reduce actual capacity and battery lifespan.

What factors affect battery capacity and runtime?

Battery runtime is affected by temperature (cold reduces capacity), age and cycle count, discharge rate (higher currents reduce effective capacity), depth of discharge, and battery chemistry. This calculator provides estimates based on ideal conditions with chemistry-specific DoD applied.

How does battery type affect usable capacity?

Different chemistries have different recommended depths of discharge. Lithium (LiFePO4/Li-ion) batteries can typically be discharged to 80–100% of their rated capacity. Lead acid batteries should only be discharged to about 50% to preserve battery life. NiCd and NiMH batteries are typically discharged to about 70–80%.

How long does it take to fully charge a 200 Ah battery?

Charging time depends on the charger output current. Using the formula: Charge Time (hrs) = Capacity (Ah) ÷ Charger Current (A). A 200 Ah battery charged at 20 A would take approximately 10 hours. Always account for charger efficiency (typically 85–95%).

How do I convert between mAh, Ah, Wh, and kWh?

1 Ah = 1,000 mAh. To convert Wh to Ah, divide by voltage: Ah = Wh ÷ V. To convert kWh to Wh, multiply by 1,000. This calculator accepts all four units and converts them automatically before computing results.

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