Battery Capacity Fade Calculator

Before entering values

Record chemistry, temperature, state of charge, age, and discharge rate. If operating conditions changed between readings, calculate separate cases.

A prefix error can move the result by several orders of magnitude. A later remaining voltage decision can draw on Capacitor Discharging Calculator.

Initial capacity

Default example: 100 Ah. Enter initial capacity in Ah.

Capacity fade

Default example: 18%. Enter capacity fade in %.

Common entry mistakes

Values recorded at different operating points should not share one case.

Recheck decimal placement and unit conversion when the answer looks unusual.

Remaining capacity: calculation method

Here, Remaining capacity is obtained from remaining = initial × (1 − fade). The entered quantities are Initial capacity and Capacity fade.

With the current entries, the primary answer is 82.00 Ah. Preserve the raw inputs when replacing this example.

Calculate remaining capacity from initial capacity and capacity fade. Pair this page with Battery Self-Discharge Calculator when reviewing capacity remaining.

Applying the result

Interpret Remaining capacity on the same basis used for the source values. Compare it with manufacturer discharge data at the intended rate.

Store the measurement state and conversion notes with the answer.

Changing Initial capacity

Change Initial capacity from 100 Ah to 120 Ah with every other entry unchanged. The result changes from 82.00 Ah to 98.40 Ah.

Use a separate scenario when multiple conditions change together.

What the formula leaves out

Fade is not always linear with time or cycles.

The arithmetic intentionally leaves out temperature, cell imbalance, BMS cutoffs, aging, and rate dependence. Resolve material omissions before selecting a standard size or rating.

Use voltage and capacity values from the same battery condition.

Trace the result back to its source

Begin by confirming capacity fade at the operating point represented by the other entries. Record whether it came from a meter, nameplate, data sheet, or design assumption.

After calculating remaining capacity, compare its magnitude with BMS limits, usable energy, current capability, and temperature. An independent order-of-magnitude check can reveal a misplaced decimal or unit prefix.

Document any effect handled outside this page, especially chemistry-specific limits and manufacturer test conditions. That note prevents a later reader from assuming the simple equation covered it.

Checking the measurement basis

The calculator rejects values outside its stated field limits, but a numerically valid entry can still describe the wrong condition. Confirm initial capacity and capacity fade against the original source before saving the result.

Use an additional case for chemistry-specific limits and manufacturer test conditions when that behavior is not negligible. Keep the baseline intact so the effect of each changed assumption remains visible.