Open the key fob to access the battery
Most Mercedes key fobs split into two halves along a seam that runs around the edge. Look for a small slot or indentation on the side of the fob — this is where you insert a flat tool to pry the two halves apart. A flathead screwdriver, coin, or plastic pry tool works; avoid using a sharp knife, which can slip and cut your hand.
Insert your tool gently into the slot and twist slightly to create a gap. Once you have a small opening, work your way around the perimeter, lifting a little at each point rather than forcing one spot. The two halves should separate cleanly without cracking the plastic. If you feel strong resistance, stop and look for a different seam — you may be at the wrong edge.
Inside, you will see the battery sitting in a metal or plastic holder. Note which side faces up before you remove it, because the replacement must go in the same way. Take a photo with your phone if you are unsure.
Key Takeaways
- Mercedes key fobs open by prying apart two halves along a seam, using a flathead screwdriver or coin as a lever.
- The battery type varies by model year and fob design, so check your owner's manual or the old battery itself before buying a replacement.
- Common Mercedes key batteries are CR2032, CR2025, or CR2016, all available at drugstores, supermarkets, and online retailers for under five dollars.
- The battery must go back in with the same side facing up as it was before removal, and the fob halves must click together firmly or the key will not work.
Identify the battery type and size
The battery you need depends on your Mercedes model and the year the key was made. The easiest way to find out is to look at the old battery itself — the type and size are printed on one side. Common Mercedes key batteries are CR2032 (the most frequent), CR2025, or CR2016. The numbers refer to the diameter and thickness in millimeters, so a CR2032 is slightly thicker than a CR2025.
If you cannot read the old battery or it is damaged, check your owner's manual under "Key Fob" or "Remote Control." Mercedes also publishes this information on their website by model and year. If you are still uncertain, take the old battery to a pharmacy or electronics store and ask the staff to match it — they do this routinely and will not charge you.
Do not guess and buy the wrong size. A battery that is too thin will rattle inside the fob and may not make proper contact. One that is too thick will not fit at all.
Remove the old battery and insert the new one
Lift the old battery straight up and out of its holder. Some fobs have a small metal clip or spring that holds the battery down — if yours does, gently bend it back just enough to free the battery, then return it to its original position once the new battery is in place.
Before you touch the new battery, hold it by the edges only. Oils from your skin can interfere with the electrical contact, especially on older fobs. If you have already touched the flat sides, wipe them gently on a clean, dry cloth.
Place the new battery into the holder with the same side facing up as the old one was. Push down gently until you hear or feel a small click — this means the battery is seated correctly. If there is a metal clip, make sure it rests on top of the battery to hold it in place.
Close the key fob and test it
Align the two halves of the fob so the seam is even all the way around. Press them together firmly, starting at one corner and working your way around the edge. You should hear a distinct click as the halves snap together. If they do not click or feel loose, open the fob again and check that the battery is seated properly and the clip (if there is one) is not bent.
Once the fob is closed, test it by pressing each button while standing near your Mercedes. The doors should lock and unlock, and the trunk should open. If nothing happens, open the fob again and verify that the battery is in the right direction and making firm contact with the metal terminals inside.
If the fob still does not work after you have checked the battery twice, the problem may be something other than the battery — a broken button, corroded contacts, or a damaged circuit board. In that case, you will need to have the fob serviced or replaced by a Mercedes dealer.
Where to buy replacement batteries
CR2032, CR2025, and CR2016 batteries are standard sizes sold almost everywhere. You can find them at pharmacies like CVS and Walgreens, supermarkets with pharmacy sections, hardware stores, and online retailers like Amazon. A single battery usually costs between one and three dollars; a pack of two or four costs only slightly more.
Buy a reputable brand — Energizer, Duracell, Panasonic, and Sony are all reliable. Avoid extremely cheap batteries from unknown manufacturers, which may have weaker charge or shorter lifespan. Some people keep a spare CR2032 at home after the first replacement, since these batteries are so inexpensive and the fob will eventually need another one.
When to replace the battery again
A Mercedes key battery typically lasts between three and four years with normal use. You will know it is time to replace it when the fob stops working from farther away than it used to, or when you have to press the buttons harder or multiple times to get a response. These are signs the battery voltage is dropping.
If your fob stops working suddenly with no warning, the battery may have failed completely. Try replacing it before assuming the fob itself is broken. Keep track of when you replace the battery so you have a rough idea when the next replacement might be due.
Frequently Asked Questions
Can I replace the battery myself or do I need to go to a Mercedes dealer?
You can replace it yourself — the process takes about five minutes and requires only a flathead screwdriver or coin. A dealer will do it for you, but you will pay a service fee (usually twenty to fifty dollars) plus the cost of the battery. Doing it at home saves money and time.
What happens if I put the battery in backwards?
The fob will not work. The battery has a positive side (marked with a +) and a negative side (marked with a −). If you reverse it, the electrical connection breaks and the buttons will not send a signal to your car. straightforward open the fob again and flip the battery around.
Is it safe to touch the battery with my bare hands?
Yes, these batteries are safe to handle. The voltage is too low to cause injury. However, skin oils can build up on the metal contacts and reduce conductivity over time, so it is better to hold the battery by its edges and wipe the flat sides with a clean cloth before installation.
Do I need to reprogram my key fob after changing the battery?
No. Replacing the battery does not erase the fob's programming. Once you install the new battery and close the fob, it should work when ready without any additional steps.
What should I do with the old battery?
Most pharmacies and electronics stores have battery recycling programs and will take old batteries for free. You can also check Earth911.com or call your local waste management office for drop-off locations. Do not throw batteries in the trash.