Method, assumptions and sources
The formula
1. Label average (W) = label kWh/year × 1000 ÷ 8760 hours
2. Load range (W) = label average × (real-use low … high) + other devices
3. Runtime range (h) = battery Wh × usable share (low … high) ÷ load (high … low)
Example: 600 kWh/year → 600,000 ÷ 8760 ≈ 68 W. Load range 68–103 W (100–150%). A 1,024 Wh station: 1,024 × 0.80 ÷ 103 ≈ 8.0 h up to 1,024 × 0.90 ÷ 68 ≈ 13.5 h.
Assumptions (and why)
- Real use 100–150% of the label. The EnergyGuide figure comes from a standardized test. Warm kitchens, frequent door openings and older seals increase use. The range is our assumption, not a measured value; change it in the calculator.
- Usable battery share 80–90%. Converting stored DC energy to AC loses some energy, and stations hold a small reserve. The range is our assumption, not a manufacturer figure; change it in the calculator.
- Average, not instantaneous, load. A fridge cycles on and off. The label's yearly figure already averages that cycling, which is why it is a better input than the nameplate wattage.
- Power checks are separate from runtime. Enter your fridge's running watts (nameplate) and, if your manual lists it, its startup watts. The calculator compares them with each station's continuous AC output and surge rating as stated by the maker. We never guess a fridge's startup draw.
Food-safety timing
USDA guidance (via FoodSafety.gov): a refrigerator keeps food safe for about 4 hours if unopened; a full freezer holds about 48 hours and a half-full one about 24 hours if the door stays closed. Source: FoodSafety.gov, checked 2026-11-02.
Specs
Every capacity, AC output and surge figure comes from the manufacturer's own product page, checked on the date shown on the models page. Where a maker does not state a figure, we say so instead of filling it in.
What this calculator does not do
- It does not guarantee runtime. Battery age, temperature and your fridge's condition change the result.
- It does not give electrical installation advice.
- It does not show prices, because they change daily. Check the brand's page.