Batteries
Battery Self-Discharge Calculator
Use Battery Self-Discharge when capacity remaining is the quantity you need. Enter initial capacity and monthly loss, then compare the answer with the equipment or operating limits that apply to your case.
Calculate Capacity remaining
Keep every entry on the units shown below.
Preparing the calculation
Use voltage and capacity values from the same battery condition. A source note beside each entry makes the result reproducible.
Check every prefix before entry; micro, milli, kilo, and mega are not interchangeable. If you also need remaining voltage, continue with Capacitor Discharging Calculator.
- Initial capacity
- Default example: 100 Ah. Enter initial capacity in Ah.
- Monthly loss
- Default example: 3%. Enter monthly loss in %.
From inputs to result
The arithmetic is based on remaining = initial × (1 − loss). The formula draws on Initial capacity and Monthly loss.
With the current entries, the primary answer is 97.00 Ah. Preserve the raw inputs when replacing this example.
Calculate capacity remaining from initial capacity and monthly loss. Another relevant worksheet is Battery Capacity Fade Calculator.
Changing Initial capacity
Change Initial capacity from 100 Ah to 120 Ah and preserve the rest of the case. This moves the answer from 97.00 Ah to 116.40 Ah.
Do not average the two cases if either could define an operating limit.
How to use the result
The calculated Capacity remaining is meaningful only with its input conditions attached. Compare it with BMS limits, usable energy, current capability, and temperature.
Store the measurement state and conversion notes with the answer.
Checks before using the answer
Temperature and storage duration change self-discharge.
The equation does not include temperature, cell imbalance, BMS cutoffs, aging, and rate dependence. Document which effects were checked elsewhere in the analysis.
Separate nameplate capacity from measured usable capacity.
Common questions before using the result
What does a zero entry represent?
Use zero only when it describes the physical condition. It is not a substitute for missing data.
Which operating condition belongs in this calculation?
Choose entries that describe the same case. Record chemistry, temperature, state of charge, age, and discharge rate.
What assumptions affect Capacity remaining?
Temperature and storage duration change self-discharge. A broader review should include temperature, cell imbalance, BMS cutoffs, aging, and rate dependence.
Why does the field result disagree with this page?
Recheck units and operating state before investigating voltage sag, thermal rise, charge taper, and balancing.
What is the cleanest way to test another scenario?
Keep unaffected entries fixed so the cause of the difference remains visible. Separate nameplate capacity from measured usable capacity.