Start the Car With a Dead Key Fob Battery

Last updated: June 12, 2026

The Chrysler 300 (LX, 2004–2011) came two ways, and which one you have decides what a dead key battery actually means. The vast majority are turn-key cars using Chrysler’s FOBIK — a fob with an integrated cut blade that you twist in the ignition. Only the higher-spec Keyless Enter-N-Go cars (mainly later 300C builds) have a true push-button start. On the turn-key cars a flat fob battery barely matters; on the push-button cars there is a simple backup.

Turn-Key 300: a Dead Battery Barely Affects You

If your 300 has an ignition you twist (the FOBIK fob plugs into the dash and rotates), the battery in the fob only powers the lock/unlock buttons on the remote. Starting works through the Sentry Key Immobiliser, which reads the transponder chip in the fob — and that chip needs no battery.

1. Unlock the door manually with the cut key blade (see below) if the remote buttons are dead.
2. Insert the FOBIK into the ignition slot on the dash.
3. Turn it as you always do. The Sentry Key system reads the chip and the engine cranks and starts normally.

In other words, a flat fob battery on a turn-key 300 leaves you able to start and drive — you just lose the remote buttons until you fit a new cell.

Push-Button (Keyless Enter-N-Go) 300: the Backup Start

If your 300 has a START/STOP button instead of a key slot, use the touch-to-button backup when the fob battery dies.

1. Get in with the emergency key blade (see below) and sit in the driver’s seat.
2. Press the brake pedal fully and hold it.
3. Press the nose of the fob — the end opposite the buttons — directly against the START/STOP button.
4. The button reads the transponder at close range and the engine starts. Keep your foot on the brake throughout.

Unlock the Door With the Cut Key Blade

When the remote stops responding, fall back to the metal blade.

1. On a FOBIK, the blade is part of the fob; on a push-button fob, slide the latch and pull the emergency key out.
2. Insert the blade into the driver’s door lock cylinder and turn to unlock.
3. If the alarm chirps, starting the car clears it.

Why the Chip Still Works With a Dead Battery

The Sentry Key Immobiliser energises a passive transponder in the fob via an antenna ring — around the ignition on turn-key cars, behind the button on Keyless Enter-N-Go cars. That chip is battery-free, so a flat coin cell never blocks starting; it only silences the remote-lock radio.

Replace the Coin Cell

Restore the remote buttons by fitting a fresh battery.

1. Split the fob: on a FOBIK, prise the case open at the seam; on a push-button fob, remove the emergency key first to release the cover.
2. Most 2004–2011 300 fobs use a CR2032 3V lithium coin cell.
3. Lift out the old cell, fit the new one the same way up (positive usually faces the cover), and clip the case shut.
4. Test the lock/unlock buttons standing beside the car.

Frequently Asked Questions

How do I tell which system my 300 has? If you twist a key-shaped fob in a dash slot, it is FOBIK turn-key. If you press a START/STOP button, it is Keyless Enter-N-Go.

My turn-key 300 won’t start even though the key turns. If the engine cranks but stalls and the security light flashes, the immobiliser is not reading the chip — a damaged transponder or worn ignition, not a flat fob battery. The coin cell does not affect starting on turn-key cars.

Which battery does the 300 fob take? A CR2032 3V lithium coin cell on most builds. Check the old one before buying.

Can the emergency blade start a push-button 300? No. The blade only unlocks the door. You must touch the fob nose to the START button to start a Keyless Enter-N-Go car.

The remote buttons died but the car still starts — is that normal? Yes, on a turn-key 300 that is exactly what a dead fob battery looks like. Fit a new CR2032 to get the remote working again.

If a warning light stayed on after you got going, you can look up the exact fault code on our sister site autodtcs.com to see whether it relates to the immobiliser or something unrelated.