All guides · Cooling and water
I budget the refrigerator in energy per day. The power in watts while the compressor is running does not alone tell you how much is disappearing from the battery over 24 hours.
Watts are the snapshot – Wh is the energy
A compressor refrigerator usually operates in cycles. Therefore, the current can be higher while it is cooling and lower between cooling periods. A data sheet with daily consumption is more useful for a battery budget than a single watt figure, but check the measurement conditions as well.
The temperature around the unit and the desired temperature inside affect how much it needs to work. The manufacturer's stated figure is therefore a basis for comparison under specific conditions, not a guarantee of the same consumption in every boat.
Calculation example with three different operating times
Assume a compressor power of 45 W. The table only shows the calculated energy from this load, without extra electronics or other losses:
| Percentage of the day in operation | Energy per day | Converted at 12 V |
|---|---|---|
| 25 % · 6 hours | 270 Wh | 22.5 Ah |
| 40 % · 9.6 hours | 432 Wh | 36 Ah |
| 60 % · 14.4 hours | 648 Wh | 54 Ah |
The formulas are W × hours = Wh and Wh / V = Ah. The numbers are hypothetical scenarios, not specifications for a product in the store.
Look at the entire weekend
In the scenario with 432 Wh per day, two days require 864 Wh for the refrigerator alone. Add lighting, pumps, electronics, and other consumers. Subtract only charging that is realistically available during the trip.
Use the battery's planned usable energy rather than assuming the full nominal capacity is always available. Capacity, temperature, age, and chosen reserve all factor into your planning.
Measure a normal day on board
A full 24 hours gives a better picture than a moment with the compressor turned on. Note the weather, temperature setting, and use of the unit. A battery monitor shows the boat's total net consumption; it does not automatically isolate the refrigerator's share if other consumers and chargers are also active.
If you want to know the refrigerator's share precisely, it requires measurement on the relevant circuit or a controlled measurement where other contributions are known.
Check the installation before buying more battery
- Is the ventilation carried out according to the unit's manual?
- Are the door seal and latch in good order?
- Is the temperature setting appropriate for the contents?
- Is the voltage at the unit sufficient during operation?
- Is the charging capacity large enough for the measured daily consumption?
Send the refrigerator model, battery information, and preferably a daily measurement. Then I will help assess whether the solution lies in the cooling, the charging, or the battery capacity.
Sources and manufacturer documentation
This guide was written by SejlStrøm. Technical information was verified on September 22, 2026. Always use the documentation for your specific model and version.