Battery Life Calculator

Battery runtime is calculated using the formula: Runtime (hours) = Usable Battery Energy (Wh) ÷ Total Device Power (W). First, convert your battery capacity to watt-hours (Wh). For mAh batteries: Wh = (mAh × Voltage) ÷ 1000. Then account for depth of discharge (DoD), inverter efficiency, and temperature effects. Our calculator handles all these factors automatically.

mAh (milliamp-hours) and Ah (amp-hours) measure electric charge — they tell you how much current a battery can deliver over time, but they don't account for voltage. Wh (watt-hours) is a true measure of energy, combining both voltage and current. A 5,000 mAh battery at 3.7V equals 18.5 Wh. For comparing batteries of different voltages, always use Wh. 1 Ah = 1,000 mAh. Wh = Ah × Voltage = (mAh × Voltage) ÷ 1000.

Depth of Discharge (DoD) is the percentage of a battery's capacity that has been used. A 100% DoD means the battery is fully drained. Most batteries shouldn't be discharged to 100% regularly — it dramatically shortens their lifespan. For example, lead-acid batteries typically recommend a 50% DoD for optimal longevity, while LiFePO₄ can safely handle 80–90% DoD. Our calculator factors in your chosen DoD to give a realistic, battery-friendly runtime estimate.

Temperature significantly impacts battery capacity. Cold temperatures slow down chemical reactions inside the battery, reducing available capacity — at 0°C (32°F), a battery may only deliver 85% of its rated capacity. At -20°C (-4°F), capacity can drop to 60% or less. Extreme heat (above 35°C/95°F) also degrades performance and accelerates aging. Our calculator includes a temperature coefficient to adjust runtime estimates based on environmental conditions.

An inverter is only needed when powering AC (alternating current) devices from a DC battery — for example, running a household appliance from a car battery. DC devices (like phones, laptops via DC adapter, LED lights) can connect directly without an inverter, achieving nearly 100% efficiency. When using an inverter, expect 85–95% efficiency — the rest is lost as heat. Pure sine wave inverters are more efficient but costlier than modified sine wave models.

• Reduce device power consumption — lower brightness, disable unused features
• Keep batteries at room temperature — avoid extreme cold or heat
• Use a higher capacity battery or connect multiple batteries in parallel
• Choose batteries with higher DoD tolerance like LiFePO₄
• Minimize inverter usage — use DC-powered devices when possible
• Regularly maintain batteries — keep terminals clean, check water levels (lead-acid)
• Consider a battery management system (BMS) to optimize charging and discharging

LiFePO₄ (Lithium Iron Phosphate) offers the longest cycle life — typically 2,000 to 5,000+ cycles at 80% DoD, lasting 5–10+ years with proper care. They also maintain stable voltage throughout discharge and are safer than standard Li-ion. For budget applications, AGM batteries offer 400–800 cycles at moderate DoD. Lead-acid is the most affordable upfront but has the shortest lifespan (200–600 cycles). Choose based on your budget, weight constraints, and expected usage frequency.