A user's new smartphone is not staying charged throughout the day.

Comprehensive and Detailed Explanation From Exact Extract:

Background applications can significantly drain a smartphone’s battery, even when the device is idle. A technician should first review which apps are running in the background and consuming power through the battery usage section of the OS. Disabling or restricting power-hungry apps often resolves poor battery life.

A. Storage usage doesn’t significantly affect battery life.

B. End of software support is unrelated to battery performance unless it's causing inefficient processes, which would still be secondary.

C. Charger wattage affects charging speed, not battery life after charging.