The correct answer is C. The battery.
The battery is the component that stores and provides electrical power to the phone. The battery can degrade over time and lose its capacity to hold a full charge. This can cause the phone to stop charging at a certain percentage and run out of power faster. To resolve this issue, the battery should be replaced with a new one that is compatible with the phone model and manufacturer.
To replace the battery, the customer may need to follow different steps depending on the type of phone and battery. Some phones have removable batteries that can be easily accessed by opening the back cover of the phone and sliding out the old battery. Other phones have non-removable batteries that are sealed inside the phone and require special tools and skills to open the phone and disconnect the old battery. In this case, the customer may need to contact the phone manufacturer or a professional service center for assistance.