Redirect output to file in Jenkins is not the same then in cmd for git fetch

Question

I would like to get some statistics on the data transferspeed of git fetch from our Windows Jenkins nodes. I thought of fetching a bare repo, and parsing the output of git fetch, witch keeps updating the same outputline with the progress and current speed. When I do a git fetch --all --no-tags --progress > output.txt 2>&1 from cmd without Jenkins, the output.txt will contain multiple lines stating transfer like this:

Receiving objects: 6% (4159/69305), 763.92 KiB | 640.00 KiB/s.

When I do the same from a bat step in Jenkins pipeline, those lines are missing.
bat "git fetch --all --no-tags --progress > fetch.txt 2>&1"

I also tried powershell without success:
powershell "Start-Process -FilePath \"git.exe\" -ArgumentList \"fetch --all --no-tags --progress\" -RedirectStandardOutput StdOut.txt -RedirectStandardError StdErr.txt"

Any idea how to get Jenkins to perform like normal cmd or other options to measure the transferspeed of git fetch?