A 12 V compressor fridge does not draw its rated current continuously. The compressor cycles, and daily energy use changes with ambient temperature, ventilation, thermostat setting, door openings, food load and battery voltage.
Start with the exact model
Read the rating plate and manual. Confirm whether the unit is a compressor fridge or an absorption fridge: they behave very differently on 12 V. Dometic's current compressor-fridge documentation, for example, identifies particular models as designed for 12 V operation, but the electrical specification still depends on the model.
Use watt-hours per day
If a fridge draws 5 A while the compressor runs, that is about 60 W at 12 V. If it averaged a 40% duty cycle across a day, the simplified estimate would be 60 W × 24 h × 0.4 = 576 Wh, or 48 Ah at 12 V before other losses. That is an illustration, not a default for every fridge.
Why real use changes
- High outside and cabinet temperatures increase run time.
- Poor ventilation around the condenser makes heat rejection harder.
- Warm food and frequent door opening add load.
- Low voltage or undersized cabling can reduce performance.
- Freezer settings and large fridge volume usually increase demand.
Measure your own system
A shunt-based battery monitor can show the fridge's contribution over representative 24-hour periods. Test in warm conditions and include all other loads before sizing batteries and solar.
Use the Battery Capacity Calculator, Solar Requirement Calculator and Off-Grid Days Calculator for the full plan.