Engel fridge drawing too much power?

just my words Bill....

Hello Stan,

suspect the Opti.as first.

For the test to be conclusive, you need to discharge the batteries with a known load current for much longer than a few minutes.

E.g. you could take 2x21W 12V bulbs and connect them to the batteries with an ammeter (multimeter), and jot down the battery voltage every 8 hours or so.

If the batteries were fully charged (unlikely with Opti.as in cyclic apps) and healthy (also unlikely), then they shouldn't have any problems powering the light bulbs for 24 hours.

Now you can draw a diagram with the four voltage readings versus time and compare this with the manufacturer supplied discharge diagram.

cheers, Peter

"suspect the Opti.as first. "
the batteries were fully charged (unlikely with Opti.as in cyclic apps)
and healthy (also unlikely).

If in doubt always cast aspersion on the competition's product before doing anything else. Same old Peter, trotting out the same old distorted biased rubbish in the desperate hope that people will think twice about buying known and respected brands and switch instead to your no name, no brand Chinese self-imports.

G'day Stan
As the others have said, you need to test the amps for a long period to get the full picture.
If the Engel is the same compressor as is normally used then it draws around 2 amps when running, some do vary a little fridge to fridge. You mentioned something which puzzles me a little and I have heard this before where it says they draw between, as you stated 0.5 and and 3.5 amps. Do you mean this as the average of the hourly use or the actual current draw. Unless this is clearly understood which is which then problems are harder to advise on.
I always go on the current draw because this is what can easily be tested and because the use/run time can vary enormously and flatten the battery far quicker than you thought it would.

Seeing you are travelling, perhaps the vehicle ambient temp the fridge is working in is quite warm and therefore the fridge is running far more often and for longer than you think it is. feeding fresh cooler air might nearly double battery charge run time.

If one fridge is dropping the battery voltage too low in a short time it must be the batteries are either not being charged to capacity or they are not capable of holding their design charge capacity.

PS Many battery testers will put a load on a battery and they say it is good when in fact it is not, makes you doubt battery testing people and their proficiency.
Only you can truly assess the situation of your fridge and batteries.

You need to forget the volts and start thinking about amps