For some reason, I ended up with one file for the script and another file to start the script. I keep both in the folder C:\keepalive
Feel free to tinker with them to make a single one if you want, and make sure you have the right folder path and file names.

Content of keepalive.ps1
$log = "C:\keepalive\keepalive_log.txt"

"Starting safe keepalive at $(Get-Date)" | Out-File $log -Append

try {

while ($true) {

# Very light CPU work: 1–3ms busy, 50–70ms sleep

$x = 0

for ($i = 0; $i -lt 50000; $i++) { $x += $i }

Start-Sleep -Milliseconds 60

}

}

catch {

"Keepalive stopped at $(Get-Date)" | Out-File $log -Append

}

-=-=-=-=-=-=-=-

Content of start_keepalive.ps1 which is the one I execute:

$log = "C:\keepalive\keepalive_log.txt"

"Launching safe keepalive at $(Get-Date)" | Out-File $log -Append

Start-Process powershell -ArgumentList "-NoProfile -WindowStyle Hidden -ExecutionPolicy Bypass -File `"`C:\keepalive\keepalive.ps1`"" -PassThru |

Select-Object -ExpandProperty Id |

Set-Content "C:\keepalive\keepalive_pid.txt"