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Battery planning tool
Estimate how long a portable fridge may run from a battery or power station. Use measured daily energy consumption when available, or estimate average load from running watts and duty cycle.
Runtime inputs
Start with the short form. Advanced mode exposes every assumption used by the estimate.
Planning result
Estimated planning range—
Expected estimate—
This is a planning range, not a promise of exact battery or fridge performance.
Actual runtime can vary with ambient temperature, set temperature, ventilation, food load, lid openings, cable voltage drop, battery condition, compressor behavior, and low-voltage cutoff settings.
Measured Wh/day is generally more useful when it was recorded under conditions similar to yours.
Running watts are not average consumption. The duty-cycle estimate has a major effect on the result.
AC inverter conversion and inverter idle draw can reduce runtime compared with direct DC operation.
The estimate does not prove outlet compatibility, startup-surge support, or that a starter battery will still start the vehicle.
Transparent formula
No temperature or freezer multiplier is hidden in the formula. Advanced mode lets you change the assumptions directly.
Use entered watt-hours, or multiply amp-hours by nominal voltage.
rated Wh = Ah × VApply usable capacity, then leave the planned reserve untouched.
usable Wh = rated Wh × usable % × (1 − reserve %)Divide Wh/day by 24, or multiply running watts by duty cycle.
average W = Wh/day ÷ 24Apply only the manual percentage entered in Advanced mode.
adjusted W = average W × (1 + adjustment %)Account for connection efficiency, then add inverter idle draw only for AC.
battery W = adjusted W ÷ efficiency + inverter idle WDivide usable energy by battery-side load. The uncertainty setting raises and lowers the adjusted load to create the planning range.
runtime hours = usable Wh ÷ battery-side WWorked examples
These generic examples are calculated by the same production utility used by the form above.
768 Wh becomes 622.1 Wh usable. The fridge averages 16.7 W, or 17.5 W at the battery after connection loss.
Planning range29.5 hours to 44.3 hours
Expected estimate: about 35.5 hours
The battery is 1,280 Wh rated and 1,036.8 Wh usable. Duty cycle produces 18 W before the manual adjustment and AC losses.
Planning range30.3 hours to 42.3 hours
Expected estimate: about 35.3 hours
Better input
Measured Wh/day is usually the most useful input when it was recorded under conditions similar to the planned trip. A compatible external energy meter can help, but only when it is suitable for the connection and equipment.
Manufacturer wattage is commonly running power, not average consumption. Manuals may describe test conditions, and a value recorded in a cool indoor room may not represent a hot vehicle with limited ventilation.
Connection losses
A suitable direct-DC connection commonly avoids inverter conversion. AC can still be convenient when a fridge lacks the right DC connection, but conversion efficiency and inverter idle draw reduce the energy available for cooling.
Idle draw matters most when the fridge’s average load is low. Documentation for the specific fridge, inverter, outlet, battery, and cabling takes priority over a planning default.
Real conditions
Energy use changes with ambient temperature, set temperature, refrigerator or freezer operation, ventilation, the starting temperature and amount of food, lid openings, and compressor control behavior.
Battery-side limits matter too: cable voltage drop, low-voltage cutoff, battery condition, and the outlet’s behavior can stop the fridge before the battery reaches a theoretical zero.
Input check
Runtime FAQ
Eight practical limits to understand before treating an energy estimate as a trip guarantee.
Rated battery capacity and compressor running watts are only the starting numbers.
Runtime depends on usable battery energy and the fridge’s battery-side average load. Enter both with reserve, connection loss, and uncertainty to get a planning range.
Usually, when Wh/day was measured in conditions similar to yours. Running watts describe the compressor while active and need a separate duty-cycle estimate.
Use a documented or measured value that reasonably matches the installation and operating conditions. If that is unavailable, treat any estimate as uncertain and widen the range.
Often it can increase compressor run time, but the change varies too much for a hidden universal multiplier. Use a manual adjustment only when you can justify it.
It commonly avoids inverter conversion and idle draw. The actual advantage depends on the equipment and connection, so check its documentation.
Yes. This calculator does not guarantee that a starter battery will retain enough energy to start the vehicle. Use appropriate battery protection and follow vehicle and equipment guidance.
Low-voltage cutoff, cable voltage drop, outlet control, battery behavior under load, or another protection limit can stop operation earlier.
A brief surge usually does not define average energy use, but it may determine whether an outlet, inverter, or battery can start the compressor. Runtime alone does not prove surge compatibility.
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