How To Test A Key FOB Battery With A Multimeter

In the hustle and bustle of daily life, the last thing anyone needs is the unexpected inconvenience of a dead key FOB battery. Imagine the frustration of approaching your car during a heavy downpour only to find that your key FOB is unresponsive.

Such scenarios underscore the importance of preemptive measures, including testing the key FOB battery with a multimeter. This article guides you through this simple yet crucial process, ensuring you’re never caught off-guard.

What is a Key FOB Battery?

A key FOB is a compact, handy device that allows car owners to lock and unlock their vehicles remotely. The heart of this convenience lies in a small but essential component – the battery. Key FOBs typically use coin cell lithium batteries, such as the CR2025 and CR2032 models, to power the remote functions that make our lives easier.

These batteries are known for their long life but don’t last forever. Recognizing signs of a weakening battery, such as decreased range, inconsistent performance, or the need to press buttons multiple times, is crucial.

Ignoring these signs might lead to a completely dead key FOB, potentially locking you out of your vehicle or disabling keyless ignition.

What is a Key FOB Battery

Why Test Your Key FOB Battery?

We’ve all faced those moments of dread when the key FOB fails at the most inopportune times. Proactive testing of the key FOB battery not only averts such scenarios but also ensures you’re not forced into unnecessary expenses or hassles.

With a multimeter, you can easily check the health of your key FOB battery and replace it promptly.

How To Test A Key FOB Battery With A Multimeter

To test a key FOB battery, remove it from it and set a multimeter to DC voltage for an initial voltage measurement. Analyze the results from the test to determine the battery’s health and decide whether a replacement is necessary to ensure the continuous optimal performance of your key FOB.

Tools Needed

Step 1: Remove the Battery from the Key FOB

Safety and precision are paramount. Begin by carefully opening the key FOB to access the battery. Handle the battery with care to avoid any damage or potential injury. Take note of the battery specifications, as this information will be crucial for testing and potential replacement.

Step 2: Set the Multimeter to DC Voltage

Before you begin, ensure your multimeter is set to the correct measurement. For key FOB batteries, typically lithium coin cells, you’ll want to set your multimeter to measure DC voltage.

The voltage setting is often denoted by a ‘V’ with a straight line above it. If your multimeter has multiple voltage settings, choose one that can measure at least up to 5 volts, as most key FOB batteries are 3 volts.

Step 3: Measure the Battery’s Voltage

  • Accessing the Battery

Open the key FOB carefully using a screwdriver if necessary. Some key FOBs have a small notch or slot for this purpose. Be gentle to avoid damaging the FOB or its internal components. Once opened, locate the battery. It’s usually easy to spot – a small, round, coin-like object.

  • Initial Inspection

Before testing, inspect the battery and its compartment. Look for any signs of corrosion or damage. If the battery or compartment is corroded, it might be best to replace it and clean it before proceeding.

  • Testing the Battery
  • Position the Probes: Touch the multimeter’s positive (red) probe to the battery’s positive side, typically marked with a “+” sign. Then, touch the negative (black) probe to the negative side of the battery.
  • Read the Multimeter: Observe the reading on the multimeter. A new, healthy 3V lithium coin cell battery often reads slightly above its rated voltage, such as 3.1V or 3.2V. If your battery is reading exactly 3V, it’s still in good condition, but if it falls below this, especially under 2.5V, it’s a sign that the battery is losing its charge and should be replaced soon.
  • Stable Readings: Ensure that the reading on the multimeter is stable. Fluctuating readings can indicate a problem with the battery or the multimeter’s connection.

Step 4: Evaluate the Results and Take Action

Armed with the findings from the multimeter and load tester, evaluate the data. Proactive replacement is the best action if the readings indicate a weakening battery.

This preemptive approach ensures uninterrupted use of your key FOB and averts the inconveniences of unexpected battery failures.

Can a key FOB battery affect the performance of the vehicle’s security system?

Absolutely. The key FOB is integral to the modern vehicle’s security system. A weakening or dead battery can lead to decreased responsiveness or complete failure of the remote locking and unlocking mechanism.

This can potentially leave your vehicle vulnerable, as you might not be able to lock it remotely or find yourself unable to disable the car’s alarm system. Regular testing and timely replacement of the key FOB battery ensure that your vehicle’s security system remains operational and practical.

Is there a way to recharge a key FOB battery, or do I always need to replace it?

Key FOB batteries, like those used in car remote controls, are typically coin cell batteries (such as CR2025 or CR2032). These batteries are not rechargeable and must be replaced when they run out of charge.

Attempting to recharge a non-rechargeable battery can be dangerous, leading to the battery leaking, rupturing, or even exploding. Therefore, when your key FOB starts to lose functionality or the range decreases, it’s a sign that the battery is running low and should be replaced with a new one of the same type and specification.

Always dispose of the old battery properly, following local regulations for battery disposal.


Testing a key FOB battery with a multimeter is a straightforward yet empowering practice. It instills confidence, eliminating the uncertainties and frustrations associated with unexpected battery failures.

Make this testing a regular practice, and enjoy the peace of mind that comes with being one step ahead.

Frequently Asked Questions

How often should I test my key FOB battery?

It’s advisable to test your key FOB battery every six months. Regular testing helps in the early detection of a weakening battery, allowing for timely replacement and uninterrupted use of your key FOB.

My key FOB battery shows the correct voltage. Does that mean it’s in perfect condition?

Not necessarily. A battery can show the correct voltage but still be weak. Testing the battery under load is essential for a comprehensive view of its health and lifespan.


Handle the battery with care to avoid damage. Avoid touching the battery terminals; always store and dispose of batteries according to the manufacturer’s instructions.

Alex Klein Author


Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.