I am not aware of anything I could turn off. Once the device gets into the 5%/hr drain state, nothing I disabled made much difference. Strange enough it happens when I boot from flash too and there is no ASUI installed. Since it happens with two different devices and with different batteries, it must be something which lives in the initfs.

Is that reasoning correct?

Other than that, I had done pretty much what you suggested. I reflashed my new device, installed bootmenu, DT (latest zImage) and copied the root fs from the internall mmc of my old device to the new device. Result: 5%/hr drain.

Then I did the same thing again, except my root fs was still intact so I did not have to copy it again. Also I did not install the latest zImage, but the DT .deb. Result: 0.5%/hr drain, but no way to mount samba shares, because cifs.ko fails.

I guess I will reflash my old device and install DT latest zImage. So everything will be absolutely vanilla and then proceed as you suggested.