The latest release of PowerCLI brings us improvements in managing host firmware for ESXi hosts:

1.    Backup functionality is moved to Get-VMHostFirmware cmdlet and the same is deprecated for Set-VMHostFirmware
2.    You can now backup and restore firmware for more than one host at once. In fact backup will store the host bundles in the specified folder using unique bundle name for each host. Restore will use the bundles from this folder and restore the configuration of the corresponding hosts

Here are some examples:

# Get two hosts to update
$hostList = Get-VMHost -Name <ESXi-hostname1>, <ESXi-hostname2>

# Backup host firmware for the specified hosts
$hostList | Get-VMHostFirmware -BackupConfiguration -DestinationPath C:\StoredBundles

# Put hosts in maintenance mode in order to restore the firmware
$hostList | Set-VMHost -State 'Maintenance'

# Restore firmware for the specified hosts
$hostList | Set-VMHostFirmware -Restore -SourcePath C:\StoredBundles -HostUser root -HostPassword 'pass'

VMHost               UploadUrl
——               ———
<ESXi-hostname1>        http:// <ESXi-hostname1>/tmp/configBundle.tgz
<ESXi-hostname2>        http:// <ESXi-hostname2>/tmp/configBundle.tgz

More details on host firmware functionality are available in the product help or PowerCLI online help.