Fridges and Freezers on Marine Lithium Batteries
Estimate daily energy for yacht fridges and freezers and learn how ambient temperature, insulation and duty cycle affect battery sizing.
Refrigeration is usually a continuous daily load.
If a 50W compressor runs 35% of the time:
50W x 24h x 0.35 = 420Wh/day
If hot weather pushes the duty cycle to 60%:
50 x 24 x 0.60 = 720Wh/day
That single change adds 300Wh/day.
Duty cycle changes with ambient temperature, insulation, thermostat setting, door opening, warm food, condenser ventilation, compressor condition and box size.
For tropical Queensland cruising, measure the fridge on a genuinely hot day before finalising the battery bank.
Turn the appliance into a daily energy figure
The peak wattage tells you whether the inverter and BMS can start the load. Runtime tells you what it does to the battery bank. Treat those as separate checks, then include conversion losses and the loads already running aboard.
- Measure typical watts and realistic hours per day, including standby use and cycling loads.
- Check startup surge and maximum simultaneous current against the inverter, BMS and cabling.
- Test the result against a poor-solar day and preserve a reserve for essential navigation and safety loads.