[walz]

I used an old Motorola phone for this, and yes, if it dies it won’t turn back on again until the power button is pressed. I Googled around and there’s a way to disable this behavior though, through an ADB command. The bad part is that it supposedly might get stuck in a boot loop – it tries to boot but there’s not enough battery yet, so it dies and keeps trying to boot. Over and over.

I made a second Tasker automation, so it shuts down with less than 15 percent battery. It might still get stuck in a boot loop, but eventually the solar panel will quickly charge it above 15% so that it won’t be for very long.

[WithinReason]

You can virtually power down a phone in Tasker without turning it off by shutting down all antennas and downclocking the CPU and GPU, disabling background tasks etc.

[franga2000]

Most android phones have a feature that lets you set a time at which the phone should turn itself on at a certain time. I used this as a last resort in a project with similar requirements, but I don't remember if we ever ended up testing if it worked after fully draining the battery.

[andai]

Interesting. The "power on when charging" thing appears to be a flag you can set, but not all brands support it.