Bought this after wanting this for a long time. I bought this size because I often stop at butcher shops and buy large quantities of frozen meat. The instructions say that if you use ice, keep it in the bag. I have not used ice yet because I wanted to test the function. I have plugged it in for over an hour before loading it, as instructed. Then loaded frozen and refrigerated items.What I have found is that even in mild days, when the car is parked and the motor doesn't run, the contents do not stay cold. (The ice chest is not in the sun.) My plan is to go hiking and bring my lunch and beverages, that I prefer cold, and they are lukewarm after the car has been turned off. On the other hand, I have driven > 8 hours with frozen on the bottom, refrigerated on the top, and dense foods stay mostly frozen, and less dense (like fish and fruit) defrosted almost completely.Having the chest with few items vs. full did make a difference in how much change in temperature there was. Unfortunately, my traditional chest does better at keeping food at temperature without ice with the same contents.I don't have an ice maker, so I will purchase a bag and try again, but the purchase doesn't make sense when you have a motor on a long drive, but for picnicking it does. Hopefully my cheese and fresh berries will still be good at lunch time in the forest.