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Battery Runtime Calculator

Calculate how long a battery bank or power backup system will sustain an electrical load before requiring recharging.

Ah
10 Ah1,000 Ah
V
12V48V
W
10 W5,000 W
%
20%95%
Calculation Results
Estimated Backup Runtime
4h 5m
Total Usable Energy: 1224 Wh (85% inverter efficiency)
Runtime in Hours
4.08 Hours
Runtime in Minutes
245 Minutes
Connected Load
300 Watts
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How to use the Battery Runtime Calculator

  1. 1Enter total battery capacity in Amp-hours (Ah).
  2. 2Enter system battery voltage (12V, 24V, 48V).
  3. 3Enter connected continuous load in Watts.
  4. 4Select depth of discharge (50% for Lead-Acid, 80-90% for Lithium LiFePO4).

How Battery Runtime is Calculated

Usable Watt-hours = Ah × Voltage × Depth of Discharge × Inverter Efficiency. Runtime = Usable Wh / Load Watts.

Mathematical Formula
Usable Wh = Capacity (Ah) × Voltage (V) × DoD % × Efficiency % Runtime (Hours) = Usable Wh / Load (Watts)
Formula Variables & Logic

Discharging lead-acid batteries beyond 50% significantly reduces their usable lifespan.

Worked Example: Running 300W of Devices on a 150Ah 12V Battery
Sample Calculation
Scenario: A 150 Ah 12V deep-cycle battery supporting 300W load at 80% depth of discharge with 85% inverter efficiency.
Step-by-step breakdown
  1. 1Nominal Capacity = 150 × 12 = 1,800 Wh
  2. 2Usable Energy = 1,800 × 0.80 × 0.85 = 1,224 Wh
  3. 3Runtime = 1,224 / 300 = 4.08 hours (4 hours 5 minutes)
Estimated Result
Battery backup runtime is 4 hours 5 minutes.

What affects Battery Runtime results

  • Peukert effect on lead-acid batteries at high discharge rates.
  • Ambient temperature variations.
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Frequently Asked Questions

What is Depth of Discharge (DoD)?

DoD is the percentage of a battery capacity that has been discharged. Lead-acid batteries should only be discharged to 50%, while Lithium iron phosphate (LiFePO4) can safely discharge to 85-90%.

What depth of discharge (DoD) should I use for lead-acid vs lithium batteries?

Use 50% maximum depth of discharge for flooded or AGM lead-acid batteries, and 80% to 90% DoD for Lithium Iron Phosphate (LiFePO4) systems.

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