I have 2 ESXi Hosts without vCenter. For backup the ESXi configuration I used a PowerCLI script:
Connect-VIServer [2001:DB8::10] Connect-VIServer [2001:DB8::11] $esxhost = Get-VMHost Get-VMHostFirmware -VMHost $esxhost -BackupConfiguration -DestinationPath C:\Backup
Change the IP Address with the address of yours ESXi hosts and set the DestinationPath according to your environment.
For restore the configuration use these commands:
Connect-VIServer [2001:DB8::10] $esxhost = Get-VMHost Set-VMHostFirmware -VMHost $esxhost -Restore -SourcePath C:\Backup\configBundle-[2001:DB8::10].tgz
Remember to put ESXi host in “Maintenance Mode” before restore the conf.