Battery Usable Capacity Calculator
Estimate usable DC energy and delivered AC energy from your battery's SOC, health and temperature factors.
The formula, every assumption, and the primary sources behind this tool are published on this page.
Results
Delivered AC energy: 4.617 kWh
Usable DC energy: 5.13 kWh
Available SOC interval: 60%
Applied factors
- 10 × 0.9 SOH × 0.95 temperature × 0.6 SOC interval = 5.13
- 5.13 × 0.9 inverter efficiency = 4.617
How it works
nominal_kwh = nominal_voltage × capacity_ah / 1000SOC_interval = (current_SOC − reserve_SOC) / 100DC_kWh = nominal_kwh × SOH × temperature_factor × SOC_intervalAC_kWh = DC_kWh × inverter_efficiency
SOH- State of health (0–1)
temperature_factor- Temperature capacity factor (0–1)
SOC_interval- Available SOC interval
Assumptions
- Use nameplate capacity at its rated reference conditions. Nominal V × Ah / 1000 converts to kWh; cutoff voltage is not nominal voltage.
- SOC minus reserve is the discharge interval; no extra DoD factor. AC delivery applies inverter efficiency once. The backup link passes already delivered AC energy.
- Default example: 10 kWh, SOC 80→20%, SOH 0.90, temperature factor 0.95 and inverter efficiency 0.90. All are editable assumptions.
FAQ
Why is available energy lower than nameplate capacity?
The model applies your remaining capacity fraction, temperature factor and usable SOC interval. With the default example it gives 5.13 DC kWh and 4.617 AC kWh.
Can I apply these factors to published usable AC energy?
That can count losses twice. Use the backup tool directly for already usable AC energy; this tool starts with nameplate energy.
Does this predict cold-weather or aged battery performance?
Only under the coefficients you supply. Use your battery's data or measurements; chemistry alone does not determine a reliable temperature or aging coefficient.
Sources
- Victron Lithium Smart technical data (checked October 4, 2026) — Backs: Product-specific capacity versus temperature, voltage and current limits; no universal coefficients are inferred.
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