Calculate battery energy efficiency, energy loss, coulombic and voltage efficiency, or runtime from voltage, capacity, DoD, efficiency, and load current.

Use the same complete charge–discharge cycle and charge-weighted average voltages (energy ÷ Ah), not charger setpoints or nominal ratings.

Battery Efficiency Formula

BE = Eout / Ein × 100

Variables:

  • BE is the Battery Efficiency (%)
  • Eout is the energy delivered during discharge (Wh)
  • Ein is the energy supplied during charge (Wh)

Divide discharge energy by charge energy from the same complete cycle and multiply by 100. In this calculator, energy in Wh equals charge-weighted average voltage multiplied by charge in Ah. For variable voltage and current, use energy integrated over the cycle; nominal voltage is not a substitute.

How to Calculate Battery Efficiency?

The following steps outline how to calculate the Battery Efficiency.

  1. First, enter the average discharge voltage and the charge taken from the battery in Ah or mAh.
  2. Next, enter the average charge voltage and the charge put into the battery for the same cycle.
  3. Use BE = Eout / Ein × 100, where each energy is average voltage × charge.
  4. Finally, calculate the Battery Efficiency.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Discharge: 4 V average × 10 Ah = 40 Wh

Charge: 5 V average × 10 Ah = 50 Wh. Efficiency = 40 / 50 × 100 = 80%; energy loss = 10 Wh.

Frequently Asked Questions

What is energy density in batteries?

Volumetric energy density is energy per volume (such as Wh/L); specific energy is energy per mass (Wh/kg). They differ from energy efficiency, which compares energy delivered with energy supplied and is expressed as a percentage.

Why is battery efficiency important?

Battery energy efficiency compares energy delivered with energy supplied over a cycle. Higher efficiency means lower energy losses for the same input, but does not by itself determine battery lifespan. Runtime modes provide a simplified constant-current estimate; optional percentages default to 100% and are not recommended operating limits.

How can battery efficiency be improved?

Battery efficiency can be improved by optimizing the battery’s internal design, such as using materials that offer lower resistance and enhancing the electrolyte composition. Advanced battery management systems (BMS) can also optimize charging and discharging processes to minimize energy loss.

What impacts a battery’s energy density?

A battery’s energy density can be affected by several factors, including the type of materials used in the electrodes, the design of the battery cell, and the efficiency of the electrolyte. Innovations in battery technology, such as the development of solid-state batteries, aim to significantly increase energy density.