I know this is an old question. I found it when searching for a solution to how to back up a hyper-v machine running on Windows 10. I believe the situation is the same in Windows 10 as it was with Windows 8. So hopefully the following will be useful to anyone else facing this problem.
The bottom line is that without using third party tools you cannot backup a hyper-v machine running on Windows 8/10. The
wbadmin command that allows you to backup hyper-v machines on Windows server doesn't support backups of hyper-v machines on Windows 8/10.
However, whilst you can't backup, you can export. An export is almost as good as a backup, possibly the most significant difference is that the virtual machine won't know that it has been "backed up", so for example sql server won't know that a backup has been run which may have implications for when logs are truncated.
You can either use the Hyper-V manager GUI to do the export or if you want to do it from the command line (which you probably will if you want it run by the task scheduler) then the powershell cmdlet is:
Export-VM -Name 'VM-Name' -PATH 'C:\Export-Path'
if you want to run this from a .cmd/.bat file then it becomes:
powershell -NonInteractive -Command "Export-VM -Name 'VM-Name' -PATH 'C:\Export-Path'"
Be aware that if you are exporting to a network share then the COMPUTER running Hyper-V will need to be granted access to the network share.