Batteries
Battery State of Charge Calculator
The purpose of Battery State of Charge is to turn remaining capacity and usable full capacity into state of charge. Keep the source condition with the saved result so later comparisons remain meaningful.
Run the Battery State of Charge scenario
Replace the examples with values from the same case.
Formula used on this page
Start with the equation SoC = remaining ÷ full capacity × 100. Its variables correspond to Remaining capacity and Usable full capacity.
Using the loaded examples gives 80.00%. Your saved case should identify where each entry came from.
Calculate state of charge from remaining capacity and usable full capacity. A connected part of the work can be checked with Battery Capacity Fade Calculator.
Measurements and entries
Record chemistry, temperature, state of charge, age, and discharge rate. Write down whether each entry is measured, rated, assumed, or calculated.
Values used below a division bar must stay positive. Convert units once, retain the original reading, and verify the converted magnitude. For the companion required nominal storage calculation, open Off-Grid Battery Bank Calculator.
- Remaining capacity
- Default example: 72 Ah. Enter remaining capacity in Ah.
- Usable full capacity
- Default example: 90 Ah. Enter usable full capacity in Ah.
How to use the result
Read State of charge as the outcome of this equation, not as automatic equipment approval. Compare it with a warm, cold, new, and aged battery case where relevant.
Save the raw entries before testing another scenario. The charging time step is handled by Battery Charging Time Calculator.
Where this estimate can fail
Voltage alone may not indicate state of charge under load.
Outside the entered variables, consider chemistry-specific limits and manufacturer test conditions. Do not hide omitted behavior inside an unexplained correction factor.
Record chemistry, temperature, state of charge, age, and discharge rate.
A second scenario
Change Remaining capacity from 72 Ah to 86.39999999999999 Ah with the rest of the inputs held constant. The comparison runs from 80.00% to 96.00%.
Use a separate scenario when multiple conditions change together.
Documenting the calculation
Document remaining capacity and usable full capacity with state of charge. Keep enough context to reproduce the result later.
Carry state of charge as the raw numerical value until the final step. Apply standard sizes only after all checks are complete.
Common questions before using the result
Can I change several inputs at once?
Change one uncertain entry at a time and preserve the baseline. Record chemistry, temperature, state of charge, age, and discharge rate.
Can I select equipment from this number alone?
The calculator does not approve equipment or supply an unexplained margin. Compare against BMS limits, usable energy, current capability, and temperature.
How much precision should I keep?
Do not round between dependent calculations. Match the final display to the precision of the source data.