What is the most common use for capacitors?
Applications of capacitors
maintain power supply while batteries are being changed
A capacitor can store electric energy when it is connected to its charging circuit. And when it is disconnected from its charging circuit, it can dissipate that stored energy, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents  loss of information in volatile memory.)