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Battery Runtime Calculator

Enter a battery's capacity and voltage, your load, and depth of discharge to estimate its runtime.

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Battery Runtime Calculator

Results

Total energy
1200 Wh
Usable energy
864 Wh
Estimated runtime
8h 38min

How it works

  1. Enter your input

    Fill in the values, paste your text, or upload the file this tool works with.

  2. See results instantly

    Most tools update live as you type; a few use a single button. Either way, the result appears right on this page.

  3. Use your results

    Copy, download, or share what the tool produces — you're always in control of the output.

Privacy and processing — Runs locally in your browser. This tool does not upload your input.

What is Battery Runtime Calculator?

Enter a battery's capacity and voltage, your load, and how deeply you're willing to discharge it to estimate how long it will run.

UNDERSTAND THE TOOL

How to estimate battery runtime

The formula

Formula
runtime_h = (Ah × V × DoD × efficiency) / load_W

Depth of discharge, explained

Depth of discharge (DoD) is how much of a battery's rated capacity is safe to actually use. Lead-acid batteries are typically limited to 50% DoD to preserve their lifespan; lithium (LiFePO4) chemistries tolerate 80–100% DoD without significant degradation.

How to use it

  • Enter the battery's capacity in amp-hours and its voltage.
  • Enter the load in watts (from the device's rating, or amps × volts).
  • Set the depth of discharge and system efficiency for your setup.

Worked example

100 Ah, 12 V battery with a 100 W load

At 80% DoD and 90% efficiency, runtime is about 8.6 hours.

100 * 12 * 0.8 * 0.9 / 100 = 8.64 h

Battery runtime note

Capacity, load, DoD, and efficiency values stay local. Real runtime also depends on battery age, temperature, discharge curve, and manufacturer limits.

Frequently Asked Questions

What DoD should I use for my battery?

About 50% for lead-acid (flooded or AGM), and 80–100% for lithium (LiFePO4) — check your battery's datasheet for its specific recommendation.

Does temperature affect real-world runtime?

Yes, meaningfully — cold temperatures reduce a battery's effective capacity, sometimes substantially. This calculator assumes room-temperature, rated capacity.

What does "system efficiency" account for?

Losses in the inverter (if you're running AC loads) and wiring between the battery and the load — 90% is a reasonable default for a well-sized system.

Why is usable Wh lower than total Wh?

Usable energy is reduced by depth of discharge and system efficiency, because not all rated battery energy should or can reach the load.

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