Lots of variables ... how full is the fridge, what are the actual contents (cold cans once cooled are a lot better than lettuce
, what is the ambient temperature, what side of the boat is the sun, how often do you open the lid?
However, as a rule of thumb 1x140ah battery lasts 48 hours including water pump, some instrument usage and occasional lights.
This is from a mega-marina top up with the batteries holding 12.8 volts for quite some time, dropping 0.3 volts when the fridge kicks in.
I switch the battery at a resting voltage of 12.3 which shows 12.0, sometimes 11.9 volts with the fridge running. The battery doesn’t seem to mind 11.9 which surprises me but they are 5 years old now and the pattern repeats with no issue.
Given the variables I mentioned I am happy when the fridge is on for 10 minutes and off for 20.
p.s.
I thought that I had made a note somewhere regarding a previous boat and have just found this. It probably makes no sense but there may be some bones that you can pick out of it
I have a feeling that the the 4 amps relates to when the fridge is running but someone will be along to tell me that there is no such thing as amps or amp hours or ah.
Don’t care
My fridge runs for approx 48 hours
“Converting Watts to Amps
The conversion of Watts to Amps at fixed voltage is governed by the equation Amps = Watts/Volts
Power input: approx. 45 to 60 watts, depending on the evaporator type
So 4 amps when running, 4 ah per hour? From 60 ah potential is 15 hours. If running for 20 mins per hour = 45 hours is 2 days”