OK, here's one for all the guru's of power consumption & so on! 
Just saw mentioned on another forum: https://www.ryobi.com.au/products/details/18v-one-23l-fridge-freezer-2-x-4-0ah-kit-r18frf142
"This Kit includes 2 x 18V ONE+ 4.0Ah Batteries and an 18V ONE+ 2A Charger ... Depending on the temperature required, these batteries can provide up to 12 hours of runtime* (with a 0 °C temperature setting and 20°C ambient temperature)."
"*18V 4.0Ah battery runtime can vary depending on the mode and temperature setting selected"
Now, of course, 30 minutes is "up to 12 hours", but for the life of me I just can't make 8Ah = 12 hours runtime 
Oh &
I don't understand what you mean by the highlighted bit.
But the fridge is rated at 60W, by the manual. What that really means is anyones guess. If they are referring to the actual power consumption when the fridge compressor is running, then that means it draws 3.33A.
So without considering losses and minimum usable voltage of the battery during discharge, one 4Ah battery will power the fridge with the compressor running for 1.2 hours.
How often the compressor runs will determine maximum run time of the fridge. So to get 12 hours from a battery, the compressor will have to run a maximum of 6 minutes per hour.... If you take into consideration inefficiency losses, and how far you can drain down the battery before it is unable to operate the fridge, it will have to be even less than 6 mins/hour...... I'd say their estimate is very optimistic.
