/usr/share/livecd-rootfs/live-build/ubuntu-touch/hooks/50-upower-poweroff-percentages.chroot is in livecd-rootfs 2.525.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | #! /bin/sh
set -e
echo "Updating upower configuration..."
sed -i 's/^UsePercentageForPolicy=.*/UsePercentageForPolicy=true/' /etc/UPower/UPower.conf
sed -i 's/^CriticalPowerAction=.*/CriticalPowerAction=PowerOff/' /etc/UPower/UPower.conf
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