Most Audi key fobs use a CR2032 coin battery. This is a standard size available at any drugstore, hardware store, or grocery store. You can find it at CVS or Walgreens in Manhasset for a couple of dollars, or order a multipack online. When you buy a replacement, get a name-brand battery from Panasonic, Duracell, or Sony. Generic batteries from unknown brands sometimes test at lower voltage right out of the package, which can make you think the battery did not solve the problem when it actually did not have a full charge to begin with.

A small number of older Audi key fobs use a CR2025 battery instead. If your key is thinner than usual and the CR2032 does not seat properly, CR2025 is likely the correct size. The replacement steps are identical.

Audi has used a few different key fob designs over the years. Here is how to open the most common ones.

Flip Key (Older Models, Some A4 and Q5 Versions Before 2021)

• The flip key has a metal blade that folds out from the body. To open it, look for a small release button or slot on the side of the fob. Press the release button to extend the metal key blade all the way out. Once the blade is extended, look at the base of the fob near where the blade was stored. You will see a small slot or seam. Insert a flathead screwdriver or a coin into that slot and gently twist to separate the two halves of the casing. Do not force it. The two halves should come apart with light pressure.

Flat Key Fob (Most Current Audi Models Including 2019 and Newer Q5, Q7, A4, and A5)

• This is the more common design on current models. The flat key fob has no folding blade and looks like a smooth rectangular remote. To open it, find the small mechanical key blade hidden inside. There is usually a small button or slide on the back of the fob. Press or slide it to release the emergency key blade, which is a thin metal key that slides out from one end. Set that key aside, you will not need it for the battery swap but removing it exposes the opening point.

With the key blade removed, look at the bottom of the fob where the blade came out. You will see a small notch or seam. Insert a coin or flathead screwdriver into that notch and twist gently. The back cover will pop off. Lay it face-down on a soft surface like a cloth or napkin so you do not scratch it.

Once the fob is open, you will see the circuit board and the battery sitting in a holder. The battery is a small silver disc, about the size of a large shirt button.

Use your fingernail or a small flathead screwdriver to gently pop the old battery out of its holder. Note which side faces up. The positive side, marked with a plus sign, typically faces up toward you. Some fobs have a small clip holding the battery in place. If yours does, press the clip gently to the side while you lift the battery out.

Drop the new CR2032 in with the positive side facing the same direction as the old battery. It should click lightly into place. Do not press hard. If it is not seating easily, check that you have it oriented correctly.

Snap the back cover of the fob back on. You should hear or feel a small click when it is fully closed. Reinsert the emergency key blade if your fob has one.

That is it. The whole process takes about three minutes once you have the battery in hand.

How to Test the Key Fob After Replacement

Walk about 30 to 50 feet away from your car and press the lock or unlock button. If the car responds on the first press from that distance, the battery replacement worked. A fresh battery should give you reliable range from at least 30 feet away in an open parking lot, and often much further.

If it only works when you are standing right next to the car, the new battery may not be seated properly. Open the fob again and press the battery firmly into its holder to make sure it is making full contact.

If you put in a fresh name-brand battery and the key fob still does not work reliably, there are a few possible explanations.

The Battery Is Not Seated Properly

Open the fob again and make sure the battery is fully pressed into its holder and making clean contact on both sides.

The Fob Casing Is Not Fully Closed

If the two halves are not fully snapped together, the circuit board may not be making proper contact. Press the halves firmly together all the way around.

The Key Fob Itself Is Damaged

Key fobs can be damaged by drops, water exposure, or worn contacts over time. If the fob has been dropped on pavement or exposed to water, the circuit board inside may have damage that a new battery cannot fix. In that case, the fob needs to be replaced.

The Issue Is the Car's Receiver, Not the Key

If the battery is new, the fob looks undamaged, and you have verified the casing is properly closed, the problem may actually be with the car's receiver antenna rather than the fob itself. A quick way to test this: try using a second key fob if you have one. If the second key has the same issue, the problem is more likely on the car's side. This is less common but worth ruling out before buying a replacement fob.

If the fob needs to be replaced rather than just the battery, expect to pay between $200 and $400 for a new Audi key fob depending on the model, plus programming. The programming has to be done at a dealer or an Audi-authorized shop because the key needs to be paired to your specific car's immobilizer system. If you are in that situation, Audi Great Neck's service team can help.