Estimate battery losses with modes, exports, and tools. Compare loaded and open circuit values quickly. Build reliable resistance estimates for cells, labs, and projects.
| Trial | Battery | E (V) | V (V) | I (A) | R Load (Ω) | Internal Resistance (Ω) |
|---|---|---|---|---|---|---|
| 1 | AA Alkaline | 1.50 | 1.38 | 0.40 | 3.45 | 0.3000 |
| 2 | Lead Acid Cell | 2.10 | 2.04 | 2.00 | 1.02 | 0.0300 |
| 3 | 18650 Cell | 4.10 | 3.98 | 2.40 | 1.66 | 0.0500 |
| 4 | Button Cell | 3.00 | 2.70 | 0.15 | 18.00 | 2.0000 |
The core battery relation is:
E = V + I × r
Where E is electromotive force, V is terminal voltage, I is current, and r is internal resistance.
r = (E - V) / I
r = (E / I) - R
Here R is the external load resistance.
r = E / Isc
Here Isc is the short circuit current.
Internal power loss = I² × r
Voltage efficiency = (V / E) × 100
Internal resistance is the opposition inside a battery. It limits current flow. It also causes voltage drop under load. A fresh battery usually has lower internal resistance. An aged battery often has higher resistance. This change affects performance, heat, and runtime.
Battery testers often look beyond open circuit voltage. A cell can show good voltage and still perform poorly. Internal resistance reveals hidden losses. It helps compare cells, check aging, and judge load response. It is useful in laboratory work, maintenance, and product testing.
This calculator supports three common methods. The first uses open circuit voltage, terminal voltage, and current. The second uses electromotive force, external load resistance, and current. The third uses electromotive force and short circuit current. Each method solves the same hidden resistance from different known values.
Battery chemistry changes the result. Electrolyte concentration matters. Electrode surface condition matters too. Temperature also shifts resistance. Cold batteries usually show higher resistance. Low state of charge can raise it further. Sulfation, contamination, and aging can make the value rise over time.
A lower result usually means better current delivery. A higher result suggests more internal loss. The calculator also reports voltage efficiency and internal power loss when possible. These added values help you judge whether the cell wastes energy as heat during discharge.
Do not compare unlike cells carelessly. A small coin cell and a deep cycle battery behave very differently. Capacity, design, and chemistry all matter. Lithium ion cells often show very low values. Lead acid batteries can vary with charge level. Alkaline cells usually rise in resistance as they empty. Use similar test conditions for fair comparison.
Use stable measurements. Record voltage without load first. Then measure loaded voltage and current quickly. Keep units consistent. Avoid long short circuit tests. They can damage the cell. Compare results at similar temperatures. Repeating trials and averaging values often gives a better estimate.
Recheck a battery after storage, overheating, deep discharge, or long service. Those events can increase resistance. Trend data is very helpful. One reading gives a snapshot. Several readings show whether the battery is staying healthy or moving toward replacement.
It is the resistance inside the battery itself. It causes voltage drop and heat when current flows. Lower values usually support better load performance.
Electrode wear, electrolyte changes, corrosion, and sulfation can increase resistance. Storage conditions and repeated deep discharge can also worsen the value.
Yes. Cold batteries often show higher internal resistance. Warm conditions can lower it, but excessive heat may damage the battery and change later readings.
The open circuit voltage and loaded voltage method is practical for routine testing. Use the method that matches the measurements you already trust.
It can be risky. High current may damage the battery, wiring, or meter. Use it only with proper precautions and very short test duration.
It usually means weaker current delivery, more internal heating, and more voltage sag under load. Aging or low charge often explains the rise.
Power loss estimates how much energy becomes heat inside the battery. It helps explain why some cells warm up and lose efficiency under load.
Only with care. Different chemistries, capacities, and designs behave differently. Compare batteries of similar type, size, charge state, and temperature.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.