Place this in the same directory as the default Initialize-PowerCLIEnvironment.ps1 to add functions to easily connect to multiple vCenters at once.

Initialize-PowerCLIEnvironment_Custom.ps1

# Initialize-PowerCLIEnvironment_Custom.ps1
# Place this alongside the default 'Initialize-PowerCLIEnvironment.ps1' script. 
# Usage:
#   1) Call 'Update-Credentials' to create/update a ViCredentialStoreItem to securely store your username and password.
#   2) Call 'Connect-VCs' to open simultaneously connections to all the vCenters in your environment. 
#   3) Do PowerCLI things.
#   4) Call 'Disconnect-VCs' to cleanly close all ViServer connections because housekeeping.

$vCenterList = @("vcenter1","vcenter2","vcenter3","vcenter4")

function Update-Credentials {
    $newCredential = Get-Credential
    Foreach ($vCenter in $vCenterList) {
        New-ViCredentialStoreItem -Host $vCenter -User $newCredential.UserName -Password $newCredential.GetNetworkCredential().password
    }
}

function Connect-VCs {
    Foreach ($vCenter in $vCenterList) {
        Connect-ViServer -Server $vCenter
    }
}

function Disconnect-VCs {
    Disconnect-Viserver -Server * -Force -Confirm:$false
}