If you need to replace the battery in your Scion IA key, you'll need a CR2032 battery. This type of battery is also known as a coin cell battery, and it's relatively easy to find and replace. Simply pop open the key fob case and remove the old battery. Then, insert the new one making sure that the positive side (the side with the + symbol) is facing up. Once the new battery is in place, close up the case and you're good to go!