The standby time on my Droid is generally very good. I've left it a whole day easily just sitting there and still had about 3/4 battery power left. From a full charge, it should be able to make it 8-10 hours easy. I do over 12 on most days with normal usage.
If it's in a cool place, it should be even better for the battery. I'd double check to be sure no tasks/services are running. And also check that no 3rd party apps are running.
How is the battery usage normally, when it's with you?