My work iPhone 11 will run for a week in low-power mode - the battery is pretty large without the screen on with a bunch of apps keeping the CPU and cellular radio warm. I use mine mostly for MFA messages & Exchange when away from my desk and that’s a lot more power-efficient than I thought.
Yeah, I thought about low power mode but at least on my Samsung phone that kills basically all of the background apps/services, which would include any forwarding service. Or well, you can choose to allow background stuff but that's where the battery savings really kick in. I guess I haven't actually tried it with zero direct usage of the screen or phone, maybe it could last that long...
