How to Measure Internal Resistance of a Battery

Introduction: Why You Need to Measure Internal Resistance

Welcome to my guide on how to measure internal resistance in batteries. This is an important topic because knowing the internal resistance of a battery can tell you a lot about its health and performance.

If you’re one of those people who just throws out batteries when they stop working, thinking that’s all there is to it, then you need to read this article. Battery manufacturers use internal resistance as an indicator of battery health.

The higher the internal resistance, the more worn out the battery is. Measuring internal resistance can tell us whether a battery is likely to fail soon or not.

This information is crucial for anyone who relies on batteries for their work or hobbies. There are various methods used to measure internal resistance, but they all have one thing in common: they involve testing the battery under load.

This means that you need a device that can apply a load to the battery while measuring its voltage at the same time. By analyzing this data, we can calculate the internal resistance.

Brief Overview of Methods Used To Measure Internal Resistance

Let’s take a brief look at some of the most popular methods used for measuring internal resistance: 1) AC Impedance Testing:

This method involves applying an AC current at different frequencies and observing how much voltage drops across the terminals. The results are plotted on an impedance graph, which gives us information about both the capacitance and inductance of the battery. 2) DC Load Testing:

This method involves applying a constant DC load across the terminals and measuring both voltage and current using specialized equipment like power analyzers or precision multimeters. 3) Pulse Load Testing:

This method involves applying short bursts of high-current pulses across the terminals and measuring voltage drop during the pulse. Pulse testing can help identify weak cells or damaged inter-cell connections. 4) Electrochemical Impedance Spectroscopy:

This method involves applying a small amplitude AC signal across the terminals and measuring the battery’s response. The data is analyzed using complex mathematical models to extract information about internal resistance, capacitance, and other electrochemical properties of the battery.

These are just some of the methods used for measuring internal resistance in batteries. We’ll dive deeper into each method later in this article, but first, let’s talk about why it’s important to measure internal resistance in the first place.

Theoretical Background

Definition and Explanation of Internal Resistance

Internal resistance is the resistance within a battery that opposes the flow of current. It is an important factor to consider in battery performance because it affects the power output and lifespan of a battery. Simply put, internal resistance occurs when energy is lost as it flows through a battery’s components.

This loss of energy leads to heat generation which can reduce the amount of energy available for use. As a result, batteries with high internal resistance will have lower power output and shorter lifespan compared to those with low internal resistance.

Factors Affecting Internal Resistance

There are several factors that can affect internal resistance, including temperature, age, chemistry, and state of charge. Temperature plays a significant role in determining internal resistance because it affects the rate at which chemical reactions occur within a battery.

As temperature increases, so does the rate of reaction which leads to higher internal resistance and reduced battery performance. Age is another factor that affects internal resistance as batteries naturally degrade over time due to usage and exposure to environmental factors.

This degradation leads to increased internal resistance and reduced overall performance. Chemistry also plays a significant role in determining internal resistance as different types of batteries have different chemical compositions that impact their overall performance.

State of charge refers to how much energy is currently stored within a battery. As batteries discharge or charge, their state of charge changes which can impact their overall performance by affecting their internal resistance.

Calculation of Internal Resistance

Internal resistance can be calculated using Ohm’s Law which states that voltage = current x resistance. By measuring the voltage across a known load resistor and calculating the current flowing through the circuit, we can calculate the total equivalent series circuit (ESC) impedance which includes both external load impedance as well as internal series impedance (internal resistances). The ESC impedance can then be subtracted from the external load impedance to obtain the internal resistance.

Another way to calculate internal resistance is to measure the voltage drop across a known current and then calculate the equivalent series circuit (ESC) impedance which includes both external load impedance as well as internal series impedance (internal resistances). This ESC impedance can then be subtracted from the battery’s open circuit voltage to obtain its internal resistance.

Understanding the theoretical background of internal resistance is crucial in ensuring optimal battery performance. By knowing what it is, what factors affect it, and how it can be calculated, we can better understand a battery’s behavior and make informed decisions about its use and maintenance.

Equipment Required

List of equipment required to measure internal resistance

To accurately measure the internal resistance of a battery, you will need several pieces of equipment. The most essential equipment is a multimeter, which is an electronic measuring instrument that measures various properties such as voltage, current, and resistance. It is crucial to invest in a good quality multimeter that has at least a 4-digit display to ensure accurate measurements.

In addition to the multimeter, you will also need two test leads with alligator clips on both ends. These leads will allow you to connect your battery and multimeter together securely.

Without these leads, your measurements could be inaccurate and potentially dangerous. Another important piece of equipment that you will need is an adjustable load resistor or power resistor that can handle the voltage and current levels of the battery being tested.

This resistor provides a load on the battery during testing and helps simulate real-world scenarios. You will also require safety gear such as insulated gloves and goggles since working with batteries can be dangerous.

Detailed explanation and function of each equipment

Let’s look at each piece of equipment in more detail: Multimeter: As mentioned earlier, a good quality digital multimeter is essential for measuring internal resistance accurately.

It measures voltage and current flow through the circuit by passing small amounts of current through it. Test Leads: Test Leads are used along with multimeters for electrical testing purposes to connect one end to an electrical device or circuit under test while using another end for connecting the device under test directly or indirectly via adapters or cables.

Adjustable Load Resistor: An adjustable load resistor provides an electrical load on your battery being tested during measurement. It simulates actual usage scenarios in real-world applications such as automotive or aviation devices where batteries undergo varying loads over time.

Insulated Gloves: When handling batteries or any other electrical components, it is essential to wear protective gear such as insulated gloves that protect against electric shocks and other hazards. Safety Goggles: Safety glasses or goggles also provide another level of protection when handling batteries since they can protect your eyes from any accidents or chemical spills.

Investing in high-quality equipment may seem like an unnecessary expense, but it could save you money in the long run by providing accurate measurements and avoiding damage or injury caused by faulty equipment. Remember, safety should always be your top priority when working with batteries or any other electrical components.

Methodology: Measuring Internal Resistance of a Battery

Measuring the internal resistance of a battery is an essential task to determine the health and performance of a battery. A multimeter is the most common instrument used to measure the internal resistance of a battery. Follow these step-by-step guidelines while measuring internal resistance using a multimeter:

1. Turn off all the devices that are connected to the battery. 2. Select DC Voltage mode on your multimeter.

3. Connect the negative (black) terminal of your multimeter to the negative (-) terminal of your battery. 4. Connect the positive (red) terminal of your multimeter to the positive (+) terminal of your battery.

5. Read and record voltage displayed on your multimeter. 6. Use Ohm’s law (R = V/I) to calculate internal resistance, where V is voltage, and I is current.

Tips and Tricks:

To get accurate readings while measuring Internal Resistance using a Multimeter, always keep in mind these tips: 1. Charge your battery fully before taking measurements.

2. Use high-quality probes for more accurate readings as cheap probes can lead to errors in measurement. 3. While connecting probes with terminals, make sure they’re firmly attached, or else you’ll get incorrect readings.

Common Mistakes to Avoid:

Despite being easy, measuring Internal Resistance can be tricky sometimes when one doesn’t follow standard protocols or procedures correctly:

A: Discussion on Common Mistakes

The most common mistakes that can lead to inaccurate readings include: 1. Not disconnecting all accessories from the battery while taking measurements

2. Connecting probes incorrectly or loosely 3. Taking quick measurements without considering how long it’s been since you last charged it

B: How these Mistakes can be Avoided

To avoid inaccurate readings, ensure that all accessories are disconnected from the battery while taking measurements. Always double-check the polarity when connecting probes with terminals and make sure they’re tightly connected. Charge your battery fully before measuring internal resistance.

Applications and Significance:

Measuring Internal Resistance is crucial to determine the health of a battery. It can help identify potential problems early on and save you from costly damages in the future. Here are some applications where measuring Internal Resistance is useful:

A: Explanation on How Measuring Internal Resistance Can Help

– In automotive industries, it helps diagnose charging system issues. – In aviation, it helps monitor aircraft batteries’ performance.

– In medical devices, it ensures optimal functioning of devices like pacemakers. – In renewable energy systems, it helps to optimize solar panel efficiency.

B: Discussion on How This Information is Useful

Measuring Internal Resistance can save you a lot of time and money in identifying potential issues with various types of batteries before they become serious problems. It also helps improve the overall performance of your devices by monitoring internal resistance regularly.


Measuring Internal Resistance is essential to assess battery health and performance. With proper methodology and taking care of common mistakes mentioned above, one can get accurate readings using a Multimeter. Measuring Internal Resistance will not only result in improved device performance but also extend battery life significantly.