🔋 Battery Life Calculator
Two modes: calculate device battery runtime (mAh ÷ mA draw), or size an off-grid battery bank for solar, RV, or backup power systems.
Frequently Asked Questions
Runtime (hours) = Battery Capacity (mAh) ÷ Device Current Draw (mA). For example, a 4000 mAh battery powering a device that draws 500 mA will last 8 hours. This is theoretical; real-world runtime is typically 10–20% less due to battery aging, temperature, and discharge rate effects.
DoD is the percentage of a battery's capacity that can be safely used. Lead-acid batteries should not be discharged below 50% DoD to preserve lifespan (2–5 years). Lithium (LiFePO4) batteries can safely discharge to 80–90% DoD with 10+ year lifespan. The calculator accounts for DoD when sizing your battery bank.
Required Ah = (Daily Load in Wh × Days of Autonomy) ÷ (Battery Voltage × DoD × Efficiency). For example: 2000 Wh/day × 2 days ÷ (12V × 0.80 × 0.95) ≈ 439 Ah. You would need at least 5 × 100Ah batteries for a 12V system.
Lithium Iron Phosphate (LiFePO4) is increasingly popular: lighter, 80%+ DoD, 3000–5000 cycles, and 10+ year lifespan, but more expensive upfront. Sealed AGM lead-acid is cheaper upfront but heavier, limited to 50% DoD, and 300–500 cycles. For long-term off-grid use, lithium offers better value.
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