Hi there,
There isn't a command in Alfred to start and stop the remote server, but I think this is a good opportunity to reassure you that having the server running won't impact battery life.
Alfred Remote Server does nothing at idle. Any activations are interrupt or notification based, so it will happy sit using 0% CPU until it's needed. Therefore, alongside other idle default OS X services which are waiting for network connections, having Alfred Remote Server running when you aren't using it won't use any additional battery on your Mac Laptop.
When it comes to your iOS device, I have specifically engineered Alfred Remote on iOS to disconnect from the server when the app isn't visible on your iOS device. At this point, Alfred Remote yields to iOS and is placed into an inactive state. So again, this won't be using any additional battery.
Cheers,
Andrew