How to Test a Battery Using a Multimeter

Knowing how to test a battery using a multimeter is important to ensure the battery is working at optimal levels and is not showing symptoms of wearing out. A battery failure can lead to seemingly increasing problems in the hardware of an electronic system or starting troubles in a car. A multimeter can be used to check the voltage and current produced by a cell which helps to recognize a faulty battery that may be replaced. The symptoms of a poor battery and how to test a battery with a multimeter are discussed below.

Table of contents

• How to check battery voltage using a multimeter
• How to check battery current using a multimeter
• How to test a car battery with a multimeter
• How to test AAA and AA batteries with a multimeter
• How to test a lithium battery with a multimeter
• FAQs

Symptoms of a poor battery

Test the battery for faults if any of the following symptoms show up:

• Physical issues like leaking, heating, physically broken terminals, or bulging
• The battery is unable to hold a charge
• The battery appears to charge to 100 percent very quickly, only to see the charge getting drained off too fast
• The voltage across the battery terminals is too low compared to its rated voltage on the label.

How to check battery voltage using a multimeter

1. Disconnect the battery from the circuit.
2. Rotate the knob of the multimeter and set it to 15-20V DC voltage (a battery generates DC power). Always set the dial to a higher range than the specified voltage of the battery. For a 9V battery, selecting the 15-20V range on the multimeter dial should work fine.
3. Connect the plug of the red probe to the VΩmA port of the multimeter, and the black probe to the COM port.
4. Connect the multimeter leads to the battery’s terminals (red probe to the battery’s positive terminal and black probe to the battery’s negative terminal).
5. Take the reading on the multimeter. If the reading shows a value greater than 7V for a 9V battery, the battery is still fit to use.
6. If the reading shows a considerably low value (say <1V for a 9V battery), the battery may be faulty or dead and needs to be replaced. The battery is typically considered dead if the multimeter reads below half the voltage level specified on the battery.

How to check battery current using a multimeter

To accurately measure the instantaneous current output of a battery using a multimeter and correct the previously mentioned inaccuracies, follow these steps:

1. Prepare the battery and multimeter: Ensure the battery is disconnected from any circuit. This is to prevent any external circuitry from affecting the measurement.
2. Set up the multimeter: Set the multimeter to measure DC current. Choose the appropriate range based on the expected current draw. For instance, if anticipating a small current draw from a small battery, setting the multimeter to the 200mA range might be advisable.
3. Connect the multimeter probes correctly: Connect the red probe to the port on the multimeter designated for current measurement. This port is often labeled "A" for amperes or "mA" for milliamperes, depending on the expected current magnitude. If the multimeter has separate ports for different current ranges (e.g., mA, A), ensure to select the correct one. Connect the black probe to the common (COM) port on the multimeter.
4. Measure the current:
   1. To measure the current, one must create a circuit where the multimeter is in series with the battery and a load. A resistor has a fixed resistance (assuming temperature remains constant), so the current drawn can be easily calculated using Ohm's Law. For example, a 5V battery connected to a 10-ohm resistor would draw 0.5 amperes (A) of current (I = V/R = 5V/10Ω = 0.5A).
   2. Connect one multimeter probe (either red or black) to one of the battery terminals. Then, connect the other probe to one end of a load (e.g., a resistor, bulb, or the device intended to be powered by the battery). Finally, ensure the other end of the load is connected back to the remaining battery terminal, completing the circuit.
   3. With the multimeter correctly integrated into the circuit, turn on the battery power (if there's an on/off switch) or complete the circuit connection. The multimeter will now measure the current flowing from the battery through the load, displaying the value in amperes (A) or milliamperes (mA).

The reading on the multimeter indicates the instantaneous current being drawn from the battery by the connected load at that moment. This measurement reflects the battery's ability to supply current under the specific conditions of the test, not its total capacity (Ah or mAh). A battery's capacity rating (e.g., 100mAh) indicates how much charge it can deliver over time, not the instantaneous current measured in this test. If the measured current aligns with the expected value for the load, the battery is likely in good condition. However, this does not directly indicate the battery's total charge capacity.

How to test a car battery with a multimeter

One of the most common batteries to check are car batteries. Like any general battery, a car battery can often go bad over time or fail suddenly. Even though it is more likely to happen during extreme weather, it is always a good idea to check the car battery under normal conditions too. An automotive battery measures 12.6 V or above when fully charged, and under a running engine, the value should be 13.7 to 14.7 V.

To check if a car battery has gone bad, look out for the following symptoms:

• Horn doesn’t sound the way it used to (or the horn appears muted)
• The brightness of the lights decreases while using the horn or indicators
• The battery light gets illuminated on the dashboard
• The car has a lot of false starts
• The vehicle requires a lot of jump-starts (connecting an external power source temporarily),
• The battery has acid spillage leading to corrosion in surrounding areas.
• The car doesn’t start

How to check the voltage across a car battery using a multimeter

A car battery is usually located in the engine compartment towards one side of the engine, but can also be placed under the wheel well, the back end of the car, or even in the trunk. Refer to the owner’s manual in case of any confusion regarding the battery location. Also, access the battery terminals by looking for metal connections on the top or front of the battery. Perform the following steps sequentially to check the voltage across the car battery when the car is off:

1. Turn on the headlights for 2-3 minutes to eliminate any surface charge on the battery.
2. Turn off the lights.
3. Set the multimeter dial to 15-20V (DC voltage).
4. Connect the plug of the red probe to the VΩmA port of the multimeter and the black probe to the COM port.
5. Connect the multimeter leads to the battery’s terminals (red probe to the battery’s positive terminal and black probe to the battery’s negative terminal).
6. Take the reading on the multimeter.

If the car is off, a reading of 12.2 V-12.6 V shows that the battery is in good condition and fully charged, and if the measured voltage is less than 12.2 V, the battery is weak and may have to be replaced.

When the vehicle is turned on, the battery drives the starter motor, so more power is drawn from the battery. The voltage rating drops for a moment as soon as the car is turned on, but it shouldn't get below 10 V. If the measured voltage is below 10 V, the battery may not have sufficient turnover strength and may be prone to failure soon, hence may be either recharged or replaced.

Another way to check a car battery is by ensuring that it draws power successfully by testing its cold cramping amps (CCA). CCA rating gives an estimation of how efficiently the battery powers an engine at cold temperatures (typically anything below 32⁰F or 0⁰C).

How to test the cold cramping amps of a car battery

1. Connect the multimeter leads to the car battery terminals.
2. Set the multimeter dial to 15-20V (DC voltage).
3. Fire up the ignition of the car. Keep the engine running throughout the measurement process.
4. The reading may drop initially (say to 10V) and then return to a higher value around 12V.
5. A constant reading after the initial drop indicates a perfect battery.
6. An initial reading greater than or equal to 5V and less than 10 V suggests that the battery is slowly dying.
7. If the reading is below 5V, it is better to replace the battery.

Note: While testing the CCA of a car battery, always take the help of another person. One can control the car ignition process while the other takes the measurement.

How to test AAA and AA batteries with a multimeter

When testing a battery, it's important to observe the correct polarity (positive and negative) of the battery and the multimeter probes to avoid damaging the device or the battery.

1. Set the multimeter to measure DC voltage.
2. Turn on the multimeter and select a voltage range that is greater than the voltage of the battery being tested. For example, if you are testing a 1.5V AAA battery, select a range of 2V or higher.
3. Touch the black probe of the multimeter to the negative (-) end of the battery and the red probe to the positive (+) end of the battery.
4. Read the voltage on the multimeter display. If the voltage is close to the rated voltage of the battery, the battery is good. For example, a new AAA battery should read around 1.5V.
5. If the voltage reading is significantly lower than the rated voltage of the battery, the battery may be drained or dead and needs to be replaced.

How to test a lithium battery with a multimeter

It's important to note that Lithium-ion batteries have a limited number of charge cycles and can become damaged if discharged below a certain voltage. It is recommended to consult the manufacturer's specifications before performing a multimeter battery test.

1. Set the multimeter to measure DC voltage.
2. Identify the positive and negative terminals of the lithium battery.
3. Connect the red probe of the multimeter to the positive terminal of the battery, and the black probe to the negative terminal.
4. Check the voltage reading on the multimeter. A fully charged lithium battery should read around 4.2 volts. If the voltage reading is significantly lower than that, the battery may be discharged or damaged.
5. If you need to test the battery's internal resistance, set the multimeter to measure resistance, and touch the probes to the positive and negative terminals of the battery. The reading should be in the range of a few ohms.
6. Once you are finished testing the battery, make sure to disconnect the multimeter probes from the battery terminals in the correct order: first the black (negative) probe, then the red (positive) probe.

To learn more about multimeters, read our multimeter guide. Also, learn how to test a capacitor using a multimeter in our technical article.

FAQs

What should a 12V battery read when fully charged?

When fully charged, a 12V battery should read slightly above 12V (say 12.6V).

What is the voltage at which a car battery needs to be replaced?

The car manual indicates where the car battery should lie, which in most cases is approximately 12.6 volts.

How long should you run a car to charge the battery?

It is advisable to drive the car for around 30 minutes before stopping again so that the battery continues to charge.

For how long can a car battery remain dead and still be recharged?

There is no single answer here, as it depends on initial battery health, storage conditions, and causes of discharge. In most cases, a dead car battery can be recharged.

How to test a battery charger with a multimeter?

Set the multimeter to measure voltage, connect the positive and negative probes to the appropriate terminals, plug in the charger, and measure the voltage output.