Would be hard as different computer specs (CPU, GPU mainly) will drain battery differently.
Your best bet to actually benchmark it is to have 1 dedicated machine, and then run it with configuration as below (assumption is that all other peripherals - dvd drive, wifi, lan, etc all turned on):
- With normal spinning HDD
- With an SSD HDD (as SSD may use battery differently)
- No HDD - Running purely on DVD drive (using LiveCD)
- No HDD - Running purely on USB drive (or other external HDD)
- No HDD - Running purely on RAM Disk (boot using USB, and USB creates a RAM disk) - The only possible issue with this is that you may have to re-install the OS every single time since RAM is volatile and will be wiped everytime you powered down your laptop.
With just based on the numbers you got there, I really doubt there is a way to calculate, not to mention that you do not provide any estimate of how long is the 'current' battery time with the HDD, and other specs of your laptop that may affect the battery usage.
For CPU Power Usage (assuming intel) you can check on ark.intel.com
For GPU power usage some manufacturer will have the information of how much power they need to run
Also usually the biggest power drain (to my experience) is CPU and GPU running more than HDD usage. If you have a program that need 100% CPU and/or GPU power (eg. Gaming, BOINC or bitcoin mining or running other research tools like matlab / mathematica / etc) then those will chew through your battery like crazy, which again as I said, is a bigger concern than simply read/write operation of the HDD. Unless you don't do any CPU/GPU intensive action, and do lots of continuous moving of big chunks of files.
Hope this helps.