More laptop power saving, Ubuntu

First, make sure your chipset supports ALPM, my Asus K43SM.401 does

vi /etc/pm/config.d/sata_alpm

write this line:
SATA_ALPM_ENABLE=true

Try to plug and unplug your charger

To check:
cat /sys/class/scsi_host/host*/link_power_management_policy

it should read min_power when on battery power