A big factor will be what and how much of high specific heat things were in the fridge during each period.
Basically, the most water laden "stuff" [water itself, milk, beer etc] you have loaded, the better will be the cold retention under the same conditions.
IMO, unless into massively long duration trips in high ambient temperatures, our fridges cope sufficiently well, an aspect long accepted by many caravanners on the continent whose cars don't feature the 12 vDC feed.
Bit like on the 5 odd hour ferry, no energy anyway to the fridge and freezer compartments, and that never seemed to manifest to any issue on the countless times we did it. Luckily at home the thing could be on EHU for a couple of days pre a trip, and be loaded from the home freezer.