Lexus IS key fob battery

Key with remote in the head

1. The remote electronics sit in the plastic head of the key itself, so there is no separate fob to open.
2. Many key heads split along the side seam. Start at the small notch and pry a little at a time.
3. Replace the cell with the same face showing, and make sure the rubber keypad sits flat before closing.
4. Snap it closed and press each button. The car still starts with a dead remote battery on most of these keys, because the start chip needs no battery.

A CR1616 is 16 mm across and 1.6 mm thick. It is easy to confuse with the 20 mm CR20xx sizes, which will not fit.

Smart key (push-button start)

1. Find the small release on the edge or back of the fob and hold it while you pull out the metal emergency key.
2. Use the slot where the metal key sat. Twist, do not lever hard, and work along the seam until the halves separate.
3. Note which side of the old coin cell faces up (usually the side with the writing), lift it out with a plastic tool, and press the new one in the same way.
4. Close the case until it clicks all the way round, put the metal key back, then try the buttons and a push-button start.

Lexus smart keys usually hide the metal key behind a release button; the cover opens from the notch next to where the key sat.

A CR1632 is 16 mm across and 3.2 mm thick. It is easy to confuse with the 20 mm CR20xx sizes, which will not fit.

A CR2032 is 20 mm across and 3.2 mm thick. CR2032, CR2025 and CR2016 share the same width but not the same thickness, so a swap between them can leave a loose contact or a case that will not close.