OMNIPOD Expiration Date

I was recently given some Pods from someone who no longer could use them. There is an expiration date of March 2013 - Is this because of the batteries in the Pod??

I would imagine the battery life would be the big factor. I would also guess they are very conservative with the expiration dates and that pods most likely would have a much longer shelf life -- unless, of course, they built in something that would disable the pod after a certain date.