If your car key fob's battery has run out, replacing it is a straightforward process that can typically be done at home or with professional assistance. To proceed with a DIY replacement, you'll need to open the key fob's casing carefully, locate the battery compartment, remove the old battery safely, and insert a new one correctly. Ensure you have the right type of battery model as specified by the manufacturer for your particular key fob make and model. After replacement, test the functionality of your key fob to confirm that all features are working as intended. If you're not comfortable with this process, contact a professional service provider who specializes in automotive key fobs to perform the battery replacement for you. Remember, keeping your key fob's battery fresh is essential for its optimal performance and reliability.