Changing a key fob battery, and knowing when that's not the fix

Can you change it yourself? On most fobs, yes

Nearly every remote, flip key and smart key runs on a small coin cell behind a snap-together case. With the correct cell and a coin, you can usually swap it yourself, and the car keeps recognizing the key.

The battery is the likely suspect when the fob fades gradually instead of dying all at once. The usual clues:

• You have to stand closer to the car than you used to.
• One press used to do it; now it takes two or three.
• The small light on the fob is faint, flickers or stays dark.
• Your push-to-start car shows a key battery warning, or now and then can't find the key.
• It misbehaves on cold mornings, then behaves once it has warmed up in your pocket.

Take that last clue seriously. A lithium coin cell delivers less current when it's chilled, so a dying cell shows its age on a frosty Meridian morning and seems healthy again by lunch.

Read the battery number before you buy one

The number is printed on the face of the coin cell, and many owner's manuals list it too. Sizes common in car keys include CR2032, CR2025, CR2016, CR2450 and CR1620. The first two digits are the diameter in millimeters and the last two are the thickness in tenths of a millimeter, so a CR2032 and a CR2025 share a width but not a thickness.

Don't settle for a near match. A cell that's too thin can lose contact on a bumpy stretch of Ten Mile Road, and one that's too thick can crack a clip. A few older remotes hold two thin cells stacked together, so count what comes out, and buy a fresh package rather than one that sat in a drawer for years.

Smart keys, flip keys and remote-head keys open in different places

Where the case splits depends on the kind of key in your hand:

• Smart key for a push-to-start car: slide the release and pull out the hidden metal blade first. The slot it leaves is often where a coin goes to split the case.
• Flip key: the remote section usually separates along a seam on the side or back. Keep tools away from the hinge, where a small spring drives the blade.
• Remote-head key: some heads come apart at a seam, some have a tiny screw, and some are sealed. If you can't find a notch or a screw, stop there; prying at a sealed head only breaks it.

Wrap a screwdriver tip in tape so it doesn't chew the plastic, and twist gently instead of levering against the circuit board.

Signs the battery isn't the problem

If a fresh cell of the right size goes in and nothing improves, look elsewhere:

• Nothing responds at all, even right beside the car with a brand-new cell.
• One button works and the others don't, which usually means a worn contact under the rubber pad.
• It only works if you squeeze the case or hold it at an angle, a hint of a cracked board or a loose connection.
• There's green or white crust inside, or the key went through the washing machine.
• Lock and unlock work, yet the engine won't start or the dash reports no key. That points to the chip or the car, not the remote battery.

Then the fob has failed or lost its pairing with the car. Our key fob not working page covers those causes and what we can do at the car, from reprogramming your fob to making a new key.

When to stop and call us

Call (208) 629-0482 if the case won't open without force, a clip snaps, the fob shows any sign above, or it's your only working key and it keeps getting worse. That last case matters most: a failing single key is a lockout in waiting, so add a spare car key while it still works.

Tell us the year, make and model, where the car is, and what the fob is doing. The price is explained on the phone before we drive out, and every key and button is tested before the locksmith leaves. If the fob is dead right now and you're standing at the car, go to getting into a push-to-start car with a dead fob.

Step by step

1. 1
   Clear a tableLay a towel down so the cell and tiny parts can't roll away.
2. 2
   Open the caseRelease the blade if there is one, find the notch along the seam, and twist a coin until the halves part.
3. 3
   Photograph the old cellSnap a phone picture before lifting it out, so the new one goes in facing the same way.
4. 4
   Seat the new cellHold it by the edges, press it flat, and check that any rubber seal is still in its groove.
5. 5
   Close it and testSnap the halves together all the way around, then try every button and start the car with that fob.