How to Repair a Key Fob If you can't get your key fob to start your car, it may be time to take it to an automotive service. Before you visit an automotive keyless entry repair shop you must first confirm a few things. The most obvious reason your key fob isn't working is a dead battery. Fortunately, most key fobs use standard 3V button cell batteries that are easily found in the majority of stores. Dead Battery The battery in your key fob is responsible for charging the remote functions that let you unlock your vehicle and open the tailgate or trunk and even start your engine. The car Mobile Key Repair fob's battery will eventually fail, just like any other battery. When this happens, it can ruin your day and alter your schedule. Fortunately, you don't need to wait for your key fob to break down before taking steps to replace the battery.