Autosync will work without power bring in the cradle if you uncheck the "While plugged in" box. However, you are limited to one sync schedule. It will sync however you have the hotsync application setup. If it is setup for local, then it will attempt to sync to your PC as if it was in the cradle. If setup for modem sync, it will do that.

Are you able to sync via modem manually without intervention after starting it?