That’s just ignorant, to assume battery will be consumed because a process is running. You’re making so many assumptions.
A classic approach will be to have a spin-wait model that incorporates a long sleep. So that you’re polling once a minute, once an hour, or even once a day. And each period of activity could be strictly constrained, e.g. poll a folder, etc. Some activities would not even require WiFi/cellular, or activating display. So why would you think there would be a discernible battery drain?
Your main reason is likely because you honestly don’t know how to do this properly.