I have a Changemoore 45 travel fridge with the internal battery plugged into the 12V cig socket on the EB70s. I am running tests on it and the Bluetti + a 200 amp Bluetti solar panel to see if I can get it to run continuously day and night. The way it works, from what I can tell, is the Bluetti charges the battery in the fridge if it needs it. The fridge when charging is drawing about 27 watts in eco mode but when full will pull zero watts. I am getting about 8 hours of usable sunlight.
Right now the Bluetti will usually be run down by the next morning, and then is struggling to fully charge by the end of 8 hours of sunlight.
its a bit difficult for me to follow, what exactly your question is.
So you do have a 200W Bluetti Solarpanel, a EB70S and Fridge with internal Battery that draws about 27W when using.
You wanna know why your EB70S is empty by the end of the day, even when the internal battery of the fridge is full and connect a Solarpanel to EB70S. Right?
The Runtime really depends on the Poweroutput from the Solarpanel. I would say that the internal battery of the fridge cant run the fridge for too long so it would relativly fast drain the EB70S down.
EB70S does have ~700Wh. When calculated with 30W Powerdraw and 20W selfconsumption it lead to 14h runtime without Solarpanel. Right now, atleast here in germany, wheather isnt that great. This lead to a not so great performance of the Solarpanel. When it draws around 50W and the Solarpanel charges like 80W than its clear why the charging is that minimal.
hope this answer helped you