Tried the new fridge. Same issue. Seems to be a problem with my second battery although its showing 13v. Might have an issue with dirty connections or something similar.
Anyway...I still returning the fridge. It draws more power than my older Waeco CF-35. (2.4 amps as opposed to 1.9 amps) Also the Aldi fridge is far more sensitive to low voltage than the Waeco.
Unless anyone is interested in buying it from me...?