The thing about the ice is that even if you pre-chill everything going into the cooler, it will never get colder than when it hits the chest. If you need to add anything, the temp in the cooler goes up, as does the temperature of everything else until the ice removes the heat from the food. This is the part that everyone tends to forget...putting ice in a cooler does not "make cold", it merely absorbs heat from the surrounding air and hence the food in contact with that air. The energy is still in the cooler, it is just now within the ice. With the 12v fridge, you can keep replenishing the fridge with warm products and the refrigerant absorbs the heat and then puts it OUTSIDE the box. The difference is night and day. With your 7 day cooler, the second you add anything warmer than the ice, you do not have a 7 day cooler anymore. With the fridge, you only need a fraction of the cooler capacity as well assuming than some of your cooler contents come in cans :blush: ...take one out, put one in. Same goes for "refrigerate after opening"; you can drive around with warm mayonnaise for months and it only needs to be refrigerated once it is opened
I used to think the same about cost...I filled a 10 litre jug of phase change material (google it) and would freeze it at work in and use it on weekends. It worked fine, but the 12v fridge is an epiphany; I no longer ask how I could afford the fridge, I now ask myself how I could NOT afford it. Literally a game changer. I know this response does not really speak to your post entirely, but these are the reasons fridges are so popular. It truly is not all about the cost.