unexpected battery drain / Zune 8gb -2nd edition

I fully charge my Zune, use it for around 45min and turn it off. Two days later I go to use it and it will dimly light the low battery symbol and then die. I have tried calibrating per Microsoft's suggestions, however no change in the way it hodls the charge. I was sure it must be a bad unit. I exchanged it at the store and am continuing to expeience the same problem with the 2nd unit. When the unit is turned off after the inital use the battery still shows it is fully charged (or very close to fully). If I check it the folowng day it shows the battery being very near fully charged as if no additional drain has occurred. However, by the 3rd day it is dead. I have even been locking the device to prevent accidental button pressing that may have been turning it on. I am at my wits end! Any suggestions would be greatly apppreciated! 

UPDATED INFO:

I read somewhere that instead of the traditional way of turning off the Zune (holding the play/pause button until it shuts down) that the unit can be shut down by by holding the back button and down button simultaneously until it powers off. This article said this more of a total shut down versus the way mentioned in the directions which still consumes some power (kind of a standby even though it appears totallly off). I do not know if this is true or not, but i do know that I have been doing it this way for over a week now and have not encountered anymore problems. Each time i turn on the Zune it shows the Zune logo and seems to reboot.

Has anyone heard of this or have any expereince with this?

Does this indicate that there is something wrong with this unit and should i try to exchange or is this somewhat normal? Yes, it works but it seems like a weird workaround and I don't know if this is just going to lead to other problems later.

I shut down my Zune like this all the time.  I charged my zune listened to it for about 1 hour, then pressed the down button while pressing the back buttong and fully shut it down.  A week later I used my Zune with the same battery as when I shut it down.  It's also a great way to restart your Zune if you happen to experience it locking up on you.