It depends very much on how you cool down (how low and how long beforehand), what and how much is inside and where the thing is (outside temperature), if not at the power supply. These are several factors.
I have bridged a "no power" scenario in the vehicle with a slightly more generous power bank (just the usual from Ecoflow) - in Spain, this year at between 20-35°c (shade) (720wh is more than enough if it doesn't have to be "making ice cream").

The cooling capacity of the Mobicool MCG15 lasts for several hours without electricity. The exact time depends on the outside temperature and the number of openings. If the cooler remains closed, 1.5 hours without power is no problem at all, especially if it has been set a little cooler beforehand.

No, the cool box keeps the set temperature for max. 1 hour, in summer rather less...