How to Turn off hdd in Ubuntu(not slow down)

I'm using 500 gb of m.2 ssd in my laptop and that's more than enough to me. I want to turn off the internal hdd to save the battery of my laptop.(I can't remove from System it voids the Warranty.)

You might check out the hdparm command in terminal...

man hdparm

Especially the -B or -S options...

   -B     Get/set Advanced Power Management feature, if the drive supports
          it.  A  low  value  means aggressive power management and a high
          value means better performance.  Possible  settings  range  from
          values  1  through  127 (which permit spin-down), and values 128
          through 254 (which do not permit spin-down).  The highest degree
          of  power  management  is  attained with a setting of 1, and the
          highest I/O performance with a setting of 254.  A value  of  255
          tells  hdparm to disable Advanced Power Management altogether on
          the drive (not all drives support disabling it, but most do).

  -S     Put  the  drive  into  idle  (low-power)  mode, and also set the
          standby (spindown) timeout for the drive.  This timeout value is
          used  by  the  drive to determine how long to wait (with no disk
          activity) before turning off the spindle motor  to  save  power.
          Under  such circumstances, the drive may take as long as 30 sec‐
          onds to respond to a subsequent disk access, though most  drives
          are much quicker.  The encoding of the timeout value is somewhat
          peculiar.  A value of zero means "timeouts  are  disabled":  the
          device will not automatically enter standby mode.  Values from 1
          to 240 specify multiples of 5 seconds, yielding timeouts from  5
          seconds to 20 minutes.  Values from 241 to 251 specify from 1 to
          11 units of 30 minutes, yielding timeouts from 30 minutes to 5.5
          hours.   A  value  of  252  signifies a timeout of 21 minutes. A
          value of 253 sets a vendor-defined timeout period between 8  and
          12  hours, and the value 254 is reserved.  255 is interpreted as
          21 minutes plus 15 seconds.  Note that  some  older  drives  may
          have very different interpretations of these values.