Karen:
The answer depends on your battery capacity and how much power you use.
For example with a very simple T/T and an absorption fridge, I could go 2-3 days until I discharged my batteries below 50% the maximum you should discharge lead acid batteries for best life.
Others with a compressor fridge, use of a CPAP on an inverter overnight, furnace use, etc even with two Group 24 batteries won't last a day.
So post your battery configuration and something about your DC usage requirement.
David
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