Battery State-of-Charge (SOC) Calculator

This tool is designed for hardware engineers and hobbyists to estimate battery life without the need for expensive dedicated fuel gauge ICs. By accounting for the steep drop-off at the beginning and end of the discharge cycle, you get a much more reliable “fuel” reading.

Use this tool to:

• Map Voltage to SOC: Convert a single-cell or multi-cell voltage reading into a 0–100% capacity estimate.
• Select Chemistry Profiles: Switch between Li-ion/LiPo (3.7V nominal), LiFePO4 (3.2V nominal), Lead-Acid (2V nominal per cell), NiMH (1.2V nominal), and Alkaline (1.5V nominal) to account for their unique discharge curves and voltage plateaus.
• Account for Cell Count: Scale the results instantly for battery packs from 1S up to 12S.

Key Technical Considerations

• Default Series (S): When Lead-Acid is selected, the series count automatically defaults to 6S (the standard for a 12V battery), as each lead-acid cell is nominally 2V.
• Alkaline Linear Slope: Unlike Lithium chemistries, Alkaline cells exhibit a steady voltage drop from 1.5V down to 0.9V. This makes voltage-based SOC more reliable for Alkaline than for chemistries with a very flat plateau like NiMH.
• The NiMH Plateau: NiMH batteries spend the majority of their discharge cycle at approximately 1.2V. Consequently, small fluctuations in voltage measurement (due to temperature or ADC noise) can lead to significant jumps in the estimated SOC.

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