It appears that this doesn't work on Windows 10. I don't have Windows 10 so I can't try it, but another forum member tried it and it didn't work for him.
Revised method for uploading a .hex file to the Arduino. This is an alternate method for uploading if you have difficulties with Xloader. This version prompts for the COM port and filename.
**** Readme file 12/12/2015 ****
To use this .zip file to load a hex file into your Arduino you first need to copy your .hex file to the same directory where you unzipped this file.
Double click the AVRDUDE_Upload.bat file and a command prompt window will appear.
The first thing the command prompt window will ask for is the port that the Arudino is attached to. For example, COM1. Enter the port name on your system where the Arduino is attached.
Next the batch file executing will ask for the filename of the .hex file you want to upload. Enter the file name of the .hex file you copied into the location where you unzipped the .zip file.
Now the batch file will upload your .hex file to the Arduino.
Once finished the batch file will pause to let you look at the upload comments. Press the space bar to allow the batch file to terminate once you have examined the upload comments.
Be sure to keep all of these files in the same directory and execute the batch file from the directory where you unzipped the files.
The grblUpload.hex file included is grbl version 0.9j from the Inventables fork.
AVRDUDE_Upload.zip (251.9 KB)