It seems that if I have VMs open in VMWare workstation they all use up a bit of the host CPU as some sort of overhead. Is this avoidable?

It’s not a lot, but it takes an hour or so off the battery life on the laptop.

I’m guessing not. Any calls or tasks will be amplified by the VM environment.

Try the usual tricks, killing running tasks, preventing programs from starting etc.

I would have thought it’s unavoidable in the same way that you have System Idle Processes running on a physical PC.