How long will a 100Ah battery run an RV fridge?

Quick answer: about 18–46 hours in these examples

A 100Ah battery at 12.8V, using 80% of nominal capacity and 90% delivery efficiency, supplies 921.6Wh in this model. A 50W fridge at a 40% duty cycle averages 20W and gives 46.1 calculated hours. Running continuously at 50W gives 18.4 hours. The range comes from different assumed loads, not a measured confidence interval or a promise for your fridge.

Find the row that resembles your measured day

Which part of the example comes from a datasheet?

The Victron LFP Smart 12.8/100 datasheet lists 100Ah and 1,280Wh at 25°C, falling to 80Ah at 0°C. The 80% usable window, 90% efficiency, fridge watts and duty cycles above are our scenario inputs. A cold battery's reduced capacity is distinct from an intentionally retained charge reserve; count each loss or reserve once, using the correct model's documentation.

Why a 12V AGM example gives a different answer

For an illustrative 12V 100Ah bank, a chosen 50% discharge window and 90% delivery efficiency leave 540Wh. At the same 20W average draw that is 27 hours. Victron's AGM datasheet rates capacity at a 20-hour discharge and shows reduced capacity at higher currents. The 50% window here is a planning choice, not a universal cutoff or proof of the life of an unspecified AGM battery. Compare the specific manufacturer's discharge and cycle curves.

Check the energy budget before buying a second battery

Measure a representative 24-hour period, recording ambient conditions, meter location, temperature settings, door openings and other loads. At a steady extra 10W of inverter standby, another 240Wh/day is used even when the fridge compressor stops. If your meter is already on the battery side, do not add the same inverter loss again. Include startup capability separately: hours of stored energy do not guarantee the compressor can start.

Use the battery-bank calculator for a no-charge reserve and the solar calculator for replenishment. Neither a sunny average nor a nameplate Ah label can replace a measured load history.

Sources and calculation notes

• Victron Lithium Battery Smart datasheet — capacity, cycle-life conditions and temperature limits
• Victron AGM/Gel datasheet — discharge-rate ratings and depth-of-discharge tradeoffs
• EcoFlow runtime testing guide — capacity, efficiency, measurement points and standby loads

Documentation checked 2026-10-24. Manufacturer specifications describe the named product or range, not every battery of that chemistry. Tables are our arithmetic under stated assumptions; they are not hands-on discharge tests or product recommendations.