When the battery gets low, the indicators will flash nine times in quick sucession when you
lock or unlock the car. From this point onward, you have approximately 100 uses of the
remote central locking fob before it won't open the car any more.
Ideally the battery should be changed on every service but they can usually last 2 years.
What Parts Do I Need?
Early 600cc (1 button key) = 2x CR2016
Fortwo 450 600cc = CR1225
Fortwo 450 700cc = CR1225
Fortwo 450 Diesel = CR1225
Fortwo 451 999cc = CR2016
Fortwo 451 Diesel = CR2016
Fortwo 453 = CR2016
Forfour 453 = CR2016
Crossblade = CR1225
Roadster = CR1225
Forfour = CR2016
The Ideal Key Battery?
The best are the Renata batteries because they are factory fitted batteries for
Swatch watches and also factory fitted in most smart keyfobs as standard.
They are Swiss made cells that cost less and last longer than other imported and no name batteries.
Early One Button Keyfob
Insert a thin screwdriver into the hole in the back to release the catch, pull the cover off.
Lever the two halves apart to reveal the PCB.
Lift the PCB up to reveal the batteries. This is the only style of smart key fob that uses two batteries.
They are stacked on top of each other with the + side down.
Pull them from the clips and replace both.
Fortwo 600cc And 700cc Keyfob
Here is the key and the new battery, remove the key from any keyrings.
To say you have piles in English is unfortunate, in French, it means you have batteries.
Place a flat blade screwdriver into the back of the key and separate the two parts.
Place the screwdriver into the cutout (circled red) and lever the PCB out of the key.
This is what you will be left with, you can now access the battery.
Pry the old battery out. It is important to have your battery ready.
On one side is a pair of sprung tabs, you need to push the battery against the tabs and push down at the back to seat it correctly. Do this within 2 minutes of removing the old one.
Reassemble the key and dispose of the battery safely.
That's it for another year.
Look on the side of the key and you will see an indent, lever the key open with a coin.
With the key in two parts you can see the battery clipped into one half.
Swap the battery over with a new one and reassemble the key.