100Ah and 12V battery runtime calculator for RV loads
Estimate watt-hours and battery runtime from voltage, amp-hours, usable capacity, conversion losses and appliance duty cycle.
Battery runtime calculator
A 12.8V 100Ah pack holds 1,280Wh nominally. A planning assumption of 80% usable energy and 90% end-to-end efficiency leaves about 922Wh for loads.
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Your estimate
Duty cycle is especially important for a refrigerator. A “50W fridge” drawing 50W only 40% of the time averages about 20W, not 50W. Measure real duty cycle in your conditions before buying.
See the worked 100Ah fridge example → · Can solar replace the energy used?
What a 100Ah label can actually tell you
For a documented capacity reference, Victron lists the LFP Smart 12.8/100 at 1,280Wh at 25°C. That is stored nominal energy. Your allowed discharge window and the path to the load determine how much of it you can use. The calculator's 80% usable setting leaves a chosen 20% reserve; the 90% efficiency setting is a separate planning assumption. Neither is a measured rating for your system.
Runtime at several loads, with the same battery
These rows use 12.8V × 100Ah × 0.80 × 0.90 = 921.6Wh delivered, start fully charged, receive no charging, and exclude any load not listed. The fridge duty cycles are illustrative.
| Load scenario | Average W | Calculated hours |
|---|---|---|
| 50W fridge, on 40% of the time | 20 | 46.1 |
| 50W fridge, on 70% of the time | 35 | 26.3 |
| 50W continuous load | 50 | 18.4 |
| 50W fridge at 40%, plus 6W router and 10W additional load (all load-side) | 36 | 25.6 |
Which efficiency should you enter?
Choose one measurement boundary. If the watts describe power at an AC appliance, include inverter and other upstream losses. If a battery-side meter already records those losses, use that measured draw and do not deduct them again. Add inverter standby separately if it is absent from your meter reading. A single fixed efficiency cannot model every load.
Can you enter power-station capacity here?
A station's rated battery Wh is not its usable AC output. Convert Wh to Ah only using the matching nominal voltage; do not treat an internal high-voltage pack as a 12V battery. The power planner's product comparison accepts Wh directly and distinguishes station ratings, bare battery ratings and documented usable outlet energy.
When the answer is too optimistic
Recalculate using a hotter-day fridge measurement, lower available capacity, or your chosen end-of-trip reserve. Confirm that an inverter can start the appliance; sufficient watt-hours do not prove adequate surge power. Use observed Wh over a representative day to replace the scenario before committing to equipment.
Sources and calculation notes
- Victron Lithium Battery Smart datasheet — capacity, cycle-life conditions and temperature limits
- 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.
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No fabricated product tests or affiliate claims. Compare verified specifications before buying.