Battery powered vending machine. Possible or a pipe dream?
Sure, its just a fridge with a small amount of electronics in it.

If your vending machine did not have a fridge in it then the battery supply would last a lot longer (weeks).

A 12V battery bank made of deep cycle lead acid batteries and a 12v - 115v converter used in cars and caravans would do the trick.

Not think its really viable, as the batteries weigh a ton and the setup would be expensive considering the profit margins from lending machines is not high.