You should never try reflashing on battery empty situation as it can lead to brick. But instead you can try "sudo ./flasher -i" and leave the device charging in the cable for hour or two (white led shows but it doesnt try to boot up). And then do "sudo ./flasher -R" to boot the device up.

If the battery is totally empty the booting process eats more energy than it can charge, so you end up in rebootloop, but if you change your phone in a mode where it isn't trying to boot up (like flasher -i), then its able to charge enough power.