Duo Pro Battery & Cart - How long do they last?

[azeis]

Just picked up a Duo Pro from electroniccigarettesinc.com - the manual isn't very clear, so I'm curious if anyone has used one and knows how long I can expect the battery to last? And also how do I know when the cart needs to be changed? Just trying to get the hang of it at the moment and would like a rough estimated. Thanks!