Why run Powershell from a .BAT file just to run another .BAT file? Try this in the autoexec.bat file: how-can-i-auto-elevate-my-batch-file-so-that-it-requests-from-uac-administrator
If insist on using Powershell to do this, then start CMD.EXE (with the necessary command line options) by using the Start-Process with the -VerbRunAs switch.
Keep in mind that UAC may be involved in the privilege elevation.