It is recommended to connect to vCenter if you have that available.
In case you don't have vCenter, you need to connect to all ESX hosts directly.
You can do this with one call to the Connect-VIServer cmdlet however, as I've demonstrated in the code below:
$user = "<removed>"
$passw = "<removed>"
$VIServers = "<IP ESXi Host>", "<IP ESX Host1>", "<IP ESX Host2>", "<IP ESX Host3>", "<IP ESX Host4>", "<IP ESX Host5>", "<IP ESX Host6>"
Set-PowerCLIConfiguration -DefaultVIServerMode "Multiple" -Confirm:$false
Connect-VIServer $VIServers -user $user -Password $passw
Get-VM | Get-Snapshot | Select vm,name,description,powerstate,created,sizeMB,@{N="DaysOld";E={((Get-date)-$_.created).Days}}
Disconnect-VIServer $VIServers -Confirm:$false
Arnim