I am not sure about a cart for prepackaged Ice Cream products staying cold enough without a plug in or something.
However, for ITALIAN ICE, our carts keep the product cold for at least 8 hours with no plug in, no cold plate and no hassle. It is crazy to me for an italian ice vendor to buy a cart with cold plates or with a plug in. The ice is very solid and actually NEEDS to thaw a little bit in order to scoop properly. Also, if you put our buckets in our cart it is cold enough in there that a bottle of water would freeze if you put it in and shut the lid.
Trust me – you will be overpaying if you are only using the cart for italian ice and you get cold plates or a plug in.
If you are using it for ice cream then I am not sure. There is dairy in ice cream and it doesnt freeze as hard as Italian ice. There may be regulations regarding the temp that you mus keep the ice cream at. However, with Italian ice there is no dairy and it freezes so hard that it will stay frozen all day in our carts.
Hope this helps and good luck!