Battery Self Discharge Calculator

Inputs

Preset chemistry

Preset updates rate and Q10 defaults.

Rated capacity

Use nominal capacity at reference conditions.

Nominal voltage (optional)

Adds energy loss in Wh.

Initial state of charge

Stored charge starts from this SoC.

Self-discharge rate

Percent loss per selected base period.

Rate base period

Used to scale loss over time.

Storage time

Enter a numeric duration.

Time unit

Converted using average month and year.

Loss model

Exponential is safer for long durations.

Storage temperature

°C

Higher values usually increase loss.

Reference temperature

°C

Rate is specified near this temperature.

Q10 factor

Rate multiplier per +10°C change.

Include simple calendar aging capacity fade

Capacity fade reduces available capacity, not only stored charge.

Calendar aging rate

% / year

Used only when aging is enabled.

Example data table

Battery	Capacity (Ah)	Rate (%/month)	Temp (°C)	Time (days)	Model	Remaining SoC (approx)
Lithium-ion pack	100	2	25	60	Exponential	≈ 96%
Lead-acid battery	80	5	30	90	Exponential	≈ 83%
NiMH cells	10	20	25	30	Linear	≈ 80%

Formula used

Temperature adjustment uses a Q10 model: factor = Q10^((T - Tref)/10).

Adjusted self-discharge per base period: r = (rate% / 100) × factor.

Exponential model: Q = Q0 × (1 − r)^N, where N = t / base.

Linear approximation: Q = Q0 × (1 − r × N), clipped at zero.

Optional capacity fade: C = C0 × (1 − k × t_year).

Q is stored charge, C is capacity, and r is a fraction.

How to use this calculator

Select a preset chemistry or keep custom values.
Enter rated capacity and initial state of charge.
Set the self-discharge rate and its base period.
Choose storage duration and the loss model.
Enter storage temperature, reference temperature, and Q10.
Enable calendar aging if capacity fade matters.
Press Calculate, then export CSV or PDF.

FAQs

1) What is battery self-discharge?

It is the slow loss of stored charge while a battery is idle. Internal reactions consume charge even without a load. The rate depends on chemistry, temperature, age, and state of charge.

2) Why does temperature matter so much?

Many reaction rates rise with temperature. The Q10 model approximates this by scaling the loss rate for every 10°C change. It is a practical engineering shortcut when detailed data is unavailable.

3) Should I use the exponential or linear model?

Use exponential for longer storage or larger rates. It compounds loss and avoids impossible negatives. The linear option is a quick approximation for short times when the rate is small.

4) What does “base period” mean?

It is the time span tied to your rate, such as percent per month. The calculator converts your storage time into an equivalent number of base periods, then applies the selected model to estimate remaining charge.

5) Does self-discharge reduce battery capacity permanently?

Self-discharge mainly reduces stored charge. Capacity fade is different and reflects aging damage. This tool can include a simple calendar aging term to estimate reduced capacity during storage.

6) Why might my real measurements differ?

Real cells vary by manufacturer, condition, and SoC range. Temperature history, parasitic loads, and protection circuits can add losses. Use this output as an estimate, then calibrate with measured data.

7) What storage SoC is usually recommended?

Many lithium packs store best at moderate SoC, often around 40–60%, but guidance varies. For any specific product, follow the manufacturer’s storage instructions and safety limits.

Tip: Run one calculation, then use the export buttons for documentation.