How to check ups battery voltage with multimeter

How to check ups battery voltage with multimeter

Knowing how to check the battery with a multimeter is important to ensure that the battery is functioning optimally and shows no signs of wear. A defective battery may appear to be a hardware problem with the electronics or a car starting problem. With a multimeter, you can check the voltage and amperage of the battery to identify a defective battery that can be replaced. Symptoms of a bad battery and how to check the battery with a multimeter are explained below.

For more information on multimeters, see our multimeter guide. To learn how to test a capacitor with a multimeter, see our technical article.

Signs of a defective battery

If you experience any of the following symptoms, check the battery for damage

Physical problems such as leaking, overheating, damaged terminals or bulging.

The battery does not hold a charge

The battery appears to charge rapidly to 100%, only to find that the charge drops too quickly.

The voltage at the battery terminals is too low compared to the rated voltage indicated on the label.

Check the battery voltage with a multimeter.

Disconnect the battery from the circuit.

Turn the knob of the multimeter and adjust it to a constant voltage of 15-20 volts (the battery produces direct current). Always set the regulator to a value higher than the specified battery voltage. For a 9V battery, the 15-20V range of the multimeter should work fine.

Connect the red probe pin to the multimeter's VΩmA connector and the black probe pin to the COM connector.

Connect the multimeter leads to the battery terminals (red probe to the positive battery terminal, black probe to the negative battery terminal).

Measure the value with the multimeter. If the reading shows a value above 7V for a 9V battery, the battery is still usable.

If the reading is significantly lower (e.g., 9V battery < 1V), the battery is probably damaged or depleted and should be replaced. In general, a battery is considered discharged when the multimeter shows less than half the specified battery voltage.

Testing the battery with a multimeter

Figure 2: Testing the battery with a multimeter

Checking the battery current with a multimeter

In most cases, you can measure the battery voltage to determine if the battery is working or dead. However, to make sure the battery is supplying enough current for charging, measure the battery amperage in milliamp hours (mAh). Batteries are specified in ampere-hours and voltage. Check the voltage and ampere-hours on the battery label. For example, 12V 95Ah means that the battery supplies 12V at 95 amp-hours for one hour.

Follow the steps below to measure the amperage of the battery.

Disconnect the battery from the circuit.

Turn the multimeter scale to set it to measure DC current in the appropriate current range (select 200 mAh if the battery label says 100 mAh).

Connect the red probe connector to the multimeter's VΩmA connector and the black probe connector to the COM connector.

Connect the multimeter leads to the battery terminals (red probe to the positive battery terminal, black probe to the negative battery terminal).

Measure the value with a multimeter.

If the multimeter reading is similar to the value indicated on the battery label, the battery is functioning properly. For example, if a 100 mA battery shows a value of 98.5 mA on the multimeter, then the battery is working properly.

How to test a car battery with a multimeter

One of the most common batteries to test is a car battery. Like any other battery, a car battery can suddenly go bad or fail over time. Although this is more likely to occur in extreme weather conditions, it is recommended that car batteries be tested under normal conditions as well. The car battery measures 12.6 V or more when fully charged and should read between 13.7 and 14.7 V when the engine is running.

To check if your car battery has failed, look for the following symptoms.

The horn does not sound as loud as it used to (or the horn seems to be off).

The lights are less bright when the horn or turn signals are activated.

The battery light on the dashboard comes on.

The car has a lot of false starts.

The car needs to be started frequently (temporary connection to external power).

Acid leaks from the battery causing corrosion in the surrounding area.

The car does not want to start

Checking the car battery with a multimeter

Figure 3: Checking the car battery with a multimeter

How to check the voltage of a car battery with a multimeter

The car battery is usually located in the engine compartment, right next to the engine, but it can also be located under the wheel arches, in the back of the car or even in the trunk. If you are not sure where the battery is located, consult your owner's manual. Also, locate the battery terminals by looking for the metal connections on the top or front of the battery. With the vehicle off, perform the following steps in sequence to check the vehicle's battery voltage

Turn on the headlights for 2-3 minutes to remove surface charge from the battery.

Turn off the headlights.

Set the multimeter scale to 15-20 volts (DC voltage).

Connect the red probe pin to the multimeter's VΩmA connector and the black probe pin to the COM connector.

Connect the multimeter leads to the battery terminals (red probe to the positive battery terminal, black probe to the negative battery terminal).

Measure the value with a multimeter.

A reading of 12.2V-12.6V when the vehicle is off indicates that the battery is in good condition and fully charged; if the measured voltage is less than 12.2V, the battery is weak and may need to be replaced.

When the vehicle is started, the battery drives the starter motor and therefore draws more power from the battery. Once the vehicle has started, the voltage drops briefly but should not fall below 10V. If the measured voltage is below 10 V, the battery may not have sufficient resistance to torque and may be prone to premature failure. Therefore, it may be recharged or replaced.

Another way to check your car's battery is to make sure the current is correct by checking the cold cranking amperage (CCA), which indicates the battery's efficiency in supplying power to the engine at low temperatures (usually below 32 0 F or 0 C).

Checking the cold cranking amperage of a car battery

Connect the multimeter leads to the car battery terminals.

Set the multimeter scale to 15-20 volts (DC voltage).

Switch on the ignition of the vehicle. Keep the engine running throughout the measurement.

The reading may drop initially (e.g., to 10V) and then rise back up to a higher value of approximately 12V.

After the initial drop, a stable reading indicates that the battery is in good condition.

An initial reading greater than or equal to 5V and less than 10V indicates that the battery is slowly discharging.

If the value is less than 5V, the battery needs to be replaced.

Note: Always ask another person to help you check the CCA value of the car battery. One person can control the ignition of the vehicle while the other takes the measurement.

Common problems

What should a 12-volt battery display when fully charged?

A fully charged 12-volt battery should indicate a value slightly above 12 volts (approximately 12.6 volts).

At what voltage should a car battery be replaced?

The owner's manual will indicate where the car battery should be connected, which in most cases is around 12.6 volts.

How long should I drive the car before charging the battery?

It is recommended to drive the car for about 30 minutes before stopping again to allow the battery to charge further.

How long after a car battery has been discharged can it continue to charge?

Under normal circumstances, a car battery will last about two weeks without starting the vehicle.