Battery car key fob: How to Change the Battery in Your Key Fob

How to Change the Battery in Your Key Fob

Like anything else relying on a battery, your car key fob can die—often at the worst time. Thankfully, these batteries are easy to replace.

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Newer cars come with a key fob of some sort, whether as a separate device attached to your keyring with buttons to lock and unlock your car, or integrated into the key itself. These fobs send a wireless signal to your car to control it, and they operate on battery power. Though batteries can last anywhere from two to five years or more, if the battery in the fob is weak, you might not be able to get into the car or remotely start it (one of many possible secret uses for your key fob). The good news is, key fob battery replacement is simple. Here’s a step by step guide for how to change the battery in your key fob.

Look for the Battery Type Embossed in the Plastic

On some key fobs, the battery type will be printed on the outside. This way, you can go to the store and select your battery before you need to open up the fob. Three of the most popular brands of key fob batteries are Duracell, Energizer, and Panasonic.


Duracell 2032 Lithium Coin Battery 3V

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Energizer Batteries, 3V Lithium Coin Cell

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Panasonic 3.0 Volt Long Lasting Lithium Coin Cell Batteries

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Look for the Seam Where the Halves of the Fob Come Together

Alaina DiGiacomo/

Most key fobs open in a clamshell fashion, where two halves snap together. There will be a seam where you can split the two halves—sometimes there will even be a notch at that seam. If your car still requires you to put the key in the ignition switch, make sure you don’t hang anything from that keyring other than the fob; the weight of your house keys can wear down the ignition cylinder, which is potentially hazardous.

Gently Pry at the Seam or Notch

Alaina DiGiacomo/rd. com

When it comes to how to change the battery in your key fob, you’ll only need one tool. Using a small, thin flat-bladed screwdriver (or, sometimes, a sturdy fingernail), pry apart the two halves gently to open the fob down the middle. Most cars with key fobs and transponder keys won’t let you lock your keys inside the car, but you need to be prepared just in case the worst case happens. (By the way—if you have a habit of losing your keys, this key finder can help you out).

Look at the Battery Orientation (Positive and Negative Ends)

Alaina DiGiacomo/

The battery will usually resemble a small coin, be marked with the battery size, and have a plus and minus sign. Note carefully which direction the battery is oriented. Once you’ve purchased a new battery of the same size, it will need to go in the same way.

Pop the Old Battery Out and Place the New Battery in

Alaina DiGiacomo/

Usually, the battery will pop out of its place with the press of a finger—if you’re having trouble, that flat-bladed screwdriver will help. Insert the new battery with the same orientation of plus and minus signs.

Snap Your Key Fob Shut and Test the Fob Function

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Assembly is the reverse of disassembly—snap the fob back together and test out the buttons. Everything should be as good as new!

Now that you know how to change the battery in your key fob, learn about the unusual car features you might not know you have.

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Have you ever wondered how to change the battery in your vehicles key fob? Check out this blog and find out how EASY it is to change your key fob battery. Find a small screwdriver, a new battery, and the key fob. We have instructional videos on our YouTube channel too! We provide this service! Give us a call at 641-648-4695, we would love to help!

Take apart the key fob

Most keys have a detachable key hidden in plain sight. Look for the different colored portion of the fob. Pull on the release button to release the key. For example, in the picture below it is the silver part of the key that will remove from the fab.

On the bottom of the key fob the silver/gray part if the fob has a removeable key.This is what t should look like when the key is removed. As you can see there is a little release button on the back side of the key fob.

Pry apart the key fob

The next step will be to remove the front and back plate off. The latches are tight together to insure a solid connection. This is where you will need a small screw driver, or an item small enough to get inside the fob like in the image.

As you can see the fab is getting pried apart by the small screwdriver.

Note: The first time the battery is changed is difficult to open the fob. Work around the fob gently inserting the screwdriver and lifting up until it comes apart. Once, it is in two pieces, a front and back, its time to change the battery!

Changing the key fob battery

Now that it is open, take note of how the battery looks! The battery needs to be replace with the proper side in place to ensure it will work. It is just like any other battery, it just appears different. Make sure the positive and negative are facing in the correct direction.

This is what the battery should look like, or to some type of variant, depending on what year the key fob was made.

Put it back together

Aligning the front and back together is a crucial step because you will need to PUSH HARD!! A clicking noise happens when it is tightly together again. Test it by pushing the lock and/or unlock to make sure the fob works properly! Don’t forget to put the manual key back in and it is all good to go!

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We provide our customers and the users of YouTube with informational and instructional videos for vehicles! Make sure to go watch the videos if you need a visual reference! Make sure to subscribe to our channel to not miss out on any informational content that could help you in the future!

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Feel free to reach out to us at 641-648-4691 or email us!

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Current consumption and batteries for car alarm key fobs

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Home – Support – Articles – Current consumption and batteries of car alarm key fobs

One of the main problems facing the designer of the key fob is the trade-off between battery life and communication range. The communication range is related to the power of the transmitter and the quiescent current in sleep mode, with the buttons not pressed.

Car alarm key fobs are small in size, so the battery is most often the largest part of its insides. Keyfob batteries are often referred to by the common word “battery”.

In the recent past, the choice of batteries for key fobs was not so diverse. These were two well-known batteries A23 and A27, with a 12 volt battery. The power reserve of these elements is low, 20-40 mAh for the A27 and 40-60 mAh for the larger brother A23.

Almost all car alarm key fobs of the 90s of the last century had a guessed shape of these large elements, clearly showing through the veil of design solutions. The fact is that until relatively recently, there were neither integrated encoders that reliably operate at voltages below 5 volts, nor the ability to build an efficient transmitter operating at a low supply voltage. With the development of cellular telephony and the market for various, remotely controlled devices, the situation has changed, microelectronics manufacturers have simply flooded the market with low-voltage integrated solutions. Both processors and integrated encoders are now available with a supply voltage of less than 2 volts.

It is no problem to build a fairly powerful transmitter, using an integrated amplifier from aging cell phones. When developing modern key fobs, it became possible to use lithium disk batteries, which were actively used before in watches and other small-sized equipment. The capacity of such batteries differs from 12-volt batteries by almost an order of magnitude, 25 mAh for an A27 battery and 210 mAh for a CR2032 battery. At the same time, the volume of the battery is noticeably smaller, and the impulse load capacity is much higher. In addition, the self-discharge current of a lithium cell is many times lower.

Now we consider: the quiescent current of the “average” key fob with the HCS300 integral encoder is about 1 μA, and the current required by the encoder and transmitter when the button is pressed is 7-10 mA. Those. on a 12-volt A27 battery, the key fob should survive with an average use of 10 button presses per day, lasting about 1 second. Only 6-9 months, but in practice, often no more than 3-4 months, or two hours with a continuously pressed button. If you put a lithium cell, the life of the battery in the key fob will be several years of operation or several tens of hours of continuous pressing.

No one will like to change the battery more than once a year, besides, wherever you carry your car keys with a key fob, there is a chance of just accidental clicks in your pocket, bag, which will reduce the actual battery life. Staying in front of a car with a “dead” key fob is a bleak prospect, so there are people who have learned from bitter experience who carry a spare key fob battery in their wallet.

Lithium batteries are more expensive, but we advise, if possible, to choose key fobs with lithium batteries. However, you need to look at the size of these batteries. The abuse of reducing the dimensions of the key fob entails a dangerous minimization of the size and capacity of the battery – there are key fobs on the Russian market that, although lithium batteries are installed, are intended for watches. The capacity of such small batteries is not higher than that of 12-volt batteries that have been “trampled” above. In any case, it is better to evaluate the capacity of the available battery in the key fob you like.

There is also the traditional problem of discrepancy between the declared and real values ​​​​for batteries, or cunning data manipulation, which manufacturers without a name often sin. We do not consider options for simply fakes; manufacturers still install decent batteries in the key fobs of even the cheapest and simplest alarms.

Below are the typical capacitance values ​​of lithium batteries, most commonly found in car key fobs, with a voltage of 3 volts. Different manufacturers give different capacities for their products, but on average, from practice, you can rely on these figures:

  • CR1616 (16 mm diameter, 1.6 mm height) 35 mAh;

  • CR2016 (20 mm diameter, 1.6 mm height) 60 mAh;

  • CR2025 (20 mm diameter, 2.5 mm height) 120 mAh;

  • CR2032 (20 mm diameter, 3.2 mm height) 210 mAh;

  • CR2430 (24 mm diameter, 3. 0 mm height) 320 mAh;

  • CR2450 (20 mm diameter, 5.0 mm height) 600 mAh.

Especially a lot of trouble with a battery is delivered by two-way car alarms, especially unknown brands. Manufacturers, in pursuit of dimensions, do not hesitate to offer solutions where the battery does not live even a couple of months. Just like cartridges, you need to have spare batteries in your pocket.

Even more complex and important are the engineering decisions regarding the energy consumption of the key fobs themselves. Superheterodyne receivers with a mass of passive elements and other anachronistic solutions from the time of the invention of the radio simply gobble up any of the most expensive and capacious Durachell or Energizer. As if there are no integrated modern transceivers, there is no way to scan the air with a duty cycle of 1/100 or more, so as not to turn on the pager receiver all the time.

Four-button Pandora keychain and its two Maxell CR2025 lithium batteries

Lithium 3V Maxell CR2025 batteries used in Pandora four-button keyfobs (two batteries per keyfob)

12V GP A27 alkaline batteries used in Pandora three-button keyfobs

1. 5V GP 24A alkaline batteries used in Tomahawk car alarm key fobs

Lithium 3V batteries Varta CR2430 used in Fortress four-button car alarm key fobs

The solutions that our company uses in its two-way alarms allow you to turn on a modern economical integrated transceiver for just 1-2 milliseconds, and there will be a few seconds of pause until the next wake-up. This allows you not to delay the signal of a possible alarm for more than a couple of seconds, and at the same time save the energy of the battery in the key fob as much as possible.
True, I had to broadcast signals “everything is calm” a little more often, but they come from the car. From the point of view of saving the energy of the key fob battery, there is no difference how often the notification channel transmitter in the car should wake up. And there, a “battery” (accumulator) of a significantly larger size is under the hood, with a charge of about 55 or even 100 A / h, and it is almost impossible to plant it with such a consumer. However, there are also examples of car alarms that are so voracious even at rest, which manage to land a serviceable battery of a peacefully standing car in a couple of weeks. But this does not apply to the energy consumption of key fobs.

In the vast majority of cases, the batteries that come with car alarm key fobs are quite functional, but still they are not expensive and capacious. We recommend replacing these batteries, waiting for their discharge, with the most capacious well-known brands. Until then, put a spare battery in the glove compartment of the car.

The battery type is usually written on the back of the key fob, at least manufacturers respecting themselves and their customers do this.

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Key fob battery features

The key requirements for signaling batteries are: a high level of rated capacity and low self-discharge of the battery. The lower the self-discharge, the longer the power supply of the alarm key fob will work.

What are the types of batteries for the alarm

Depending on what type of key fob in your alarm system (main with a display or auxiliary without a display), the following batteries are used in the device:

  • Class 27A special battery.
  • Lithium battery 2032.
  • Battery 2025.

How to understand that the battery needs to be replaced

The following “signals” may indicate that the battery in the key fob is either out of order or close to it:

  • Commands are transmitted only when the button is pressed strongly.
  • The LED light on the key fob has begun to dim.
  • After pressing the buttons, the car does not react in any way.
  • A low battery alarm appeared on the remote control screen.

How to choose a quality battery

The quality of a battery is naturally determined by both the manufacturer and the type of battery.


  • Battery type. The battery can be manganese, lithium, and lithium-manganese. Older security systems use alkaline batteries.
  • Battery class. We are talking about the format (finger, tablet, special).
  • Rated voltage value. It is measured in volts and, depending on the power source, ranges from 1.5 to 12V. For devices powered by 3V it is possible to use two 1.5V batteries. Such batteries are most often used in an additional key fob that is not equipped with an LCD screen.
  • Charging container. Measured in ampere-hours (Ah)
  • Charge current. Measured in Amperes, it is intended to determine the moment of receipt of the capacity declared by the manufacturer. For some manufacturers, this parameter is not indicated; only resistance is indicated on the packaging.
  • Maximum discharge current. This is a parameter that determines the duration of the safe discharge of the battery. This setting will not cause the battery to overheat, the base of the battery will not be damaged, and the electrolyte will not leak out.