In my Ubuntu 18.10 neither udev rule or hdparms.conf works. 
Instead I needed to edit /etc/default/tlp changing DISK_APM_LEVEL_ON_BAT value.

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  Default on battery APM level causes SSD runing very slow

Status in Ubuntu:
Status in apmd package in Ubuntu:

Bug description:
  Installed Ubuntu 16.04 on a Dell 7559 laptop with Crucial MX300 750GB
  SSD. When power is unplugged, file read/write speed is about 30MB/s
  consistently. When power is plugged, file read/write speed is about
  400~500MB/s consistently.

  Used hdparm to check SSD status and found APM level is 128 on battery
  and 254 on power.

  Edited /etc/hdparm.conf to set apm_battery=254 and after reboot file
  read/write speed back to normal 400~500MB/s.

  Not sure if this is a feature or bug but on battery APM level 128 had
  caused SSD running ridiculously slow (~30MB/s).

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