The Fiat Punto uses a keyless car door-entry system, similar to many vehicles, although the key fob does contain a regular key for emergencies. Point the key fob toward the car when you are a few feet away, press the button and you unlock the doors. The key fob contains a small button cell battery that occasionally needs replacing.
Remove the Fiat Punto's key fob cover to access the emergency key. Use a small flat head screwdriver to pry off the cover. Slide the tip of the screwdriver between the cover and main part of the key fob and twist slightly. The cover pops open so you can remove it using your fingers.
Lift out the key from the recess using your fingers. This reveals a battery cover that's screwed in place. Use a small Phillips screwdriver to twist the screw counter clockwise. You don't need to remove the screw. As soon as you turn the screw the battery container opens so you can get to the battery.
Look at the battery to see how it is fitted, as you need to put the replacement battery back the same way. Button cell batteries are clearly labelled "+" on one side, indicating positive. The other side of the battery doesn't have any markings, but is the negative terminal.
Put in the replacement battery ensuring you get the polarity correct. It won't cause damage if incorrectly place, but it does mean doing it again.
Push down on the battery container slightly using your fingers, then turn the screw clockwise until it holds the battery container in place. Replace the key. Replace the key fob cover and press it until it clicks into place.