Peukert Effect

t = C / I^k

Quick answer

This calculator solves t = C / I^k for t. With Rated Capacity 20 Ah, Discharge Current 2 A, Peukert Exponent 0.5, the result is 14.14 h.

Calculator

Result
—

Formula

t = C / I^k

Description

Peukert's law describes how the effective capacity of a battery decreases at higher discharge rates. The exponent k (Peukert constant) is always greater than 1 for real batteries, meaning that doubling the discharge current more than halves the runtime. For an ideal battery k = 1, but real batteries have internal resistance and chemical kinetics that reduce available capacity under heavy load. Lead-acid batteries typically have k = 1.1-1.3, while lithium-ion batteries have k closer to 1.02-1.10, making them much better at high discharge rates.

Variables

  • t — Effective runtime in hours (h)
  • C — Rated capacity at 1A discharge rate (Ah)
  • I — Actual discharge current (A)
  • k — Peukert exponent (dimensionless, >1)

Practical Notes

The Peukert constant is determined experimentally by discharging batteries at different rates and fitting the results. It is most significant for lead-acid and NiCd batteries. For lithium-ion cells, the effect is small enough that simple capacity derating at high C-rates is often sufficient. Temperature also affects the effective Peukert constant.

Symbols and units

Symbol Meaning Default unit Accepted units
Cap Rated Capacity Ah mAh, Ah
I Discharge Current A pA, nA, µA, mA, A, kA
k Peukert Exponent — —

Step by step

  1. 1. What you know: Rated Capacity 20 Ah, Discharge Current 2 A, Peukert Exponent 0.5
  2. 2. The relation: t = C / I^k
  3. 3. Substitute: Cap = 20 Ah, I = 2 A, k = 0.5
  4. 4. Result: t = 14.14 h

Worked examples

Minimum range

Given: Rated Capacity 0.2 Ah, Discharge Current 2 mA, Peukert Exponent 0.025

Result: t = 0.2336 h

Low range

Given: Rated Capacity 2 Ah, Discharge Current 20 mA, Peukert Exponent 0.25

Result: t = 5.318 h

Typical

Given: Rated Capacity 20 Ah, Discharge Current 2 A, Peukert Exponent 0.5

Result: t = 14.14 h

High range

Given: Rated Capacity 200 Ah, Discharge Current 100 A, Peukert Exponent 0.8

Result: t = 5.024 h

Maximum range

Given: Rated Capacity 2000 Ah, Discharge Current 1 kA, Peukert Exponent 8

Result: t = 2 × 10⁻²¹ h

How t changes with Rated Capacity

Rated Capacity (input) t (result)
2 Ah 1.414 h
5 Ah 3.536 h
10 Ah 7.071 h
15 Ah 10.61 h
20 Ah 14.14 h
30 Ah 21.21 h
40 Ah 28.28 h
80 Ah 56.57 h
140 Ah 98.99 h
200 Ah 141.4 h

Embed this calculator

Paste this into any page. It keeps working when this page updates, and credits the source.

<iframe src="https://vbatpower.com/embed/peukert/" width="100%" height="460" style="border:1px solid #1f2a37;border-radius:12px" loading="lazy" title="Peukert Effect"></iframe>
<p><a href="https://vbatpower.com/formulas/peukert/">Peukert Effect</a> Calculator by vbatpower.com</p>

Frequently asked questions

How do you calculate Peukert Effect?

Use t = C / I^k. With Rated Capacity 20 Ah, Discharge Current 2 A, Peukert Exponent 0.5, t works out to 14.14 h.

How do you calculate formule de peukert kt?

Rearrange for t: with Rated Capacity 2 Ah, Discharge Current 20 mA, Peukert Exponent 0.25, t is 5.318 h.

What is the formula for Peukert Effect?

The formula is t = C / I^k. Peukert's law describes how the effective capacity of a battery decreases at higher discharge rates.

Related Concepts

All Power & Efficiency formulas →
Linear Regulator Dissipation Efficiency Buck Converter Boost Converter Peukert Effect Energy After Losses Solar Charge Time LDO Minimum Output

Need more features?

Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.

Try the App