DIY Cost: $ 3 - 10 Est. Time: 5 mins Difficulty: Very Easy Summary Step-by-step procedure on how to replace the key fob battery on a 2016-2020 Kia Optima. What you will need Pick tool Flat screwdriver CR2032 Lithium battery 3V Procedure Insert the flat screwdriver into the hole on the side of key fob. Twist the flat screwdriver to pop out the cover on the battery. Slide the battery to the side and insert a pick tool to pop out the battery of the key fob. Slide the new battery into the key fob and push it in to lock it in its place. Push the cover back until it snaps back to the key fob.