Power Station Runtime Calculator
My power plan
Equipment
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Example watts — edit to match your equipment.
64 matching items · All presets use AC input initially.
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Setup
Your battery
Station output ratings (optional)
Watt ratings alone cannot establish equipment compatibility.
Use nominal stored energy. Already measured usable output energy is not supported by this model.
Assumptions
10% reserve · 85% AC efficiency · 10% extra capacity margin
Edit charge window and losses
These defaults are editable assumptions. Reserve defines the lower charge limit; no second depth-of-discharge reduction is applied.
Estimate battery runtime for a repeating equipment load
Compare available battery energy with a continuous duty-and-standby load pattern.
Use runtime view when the main question is how long a known battery can support equipment. It repeats the entered running, duty and off-cycle pattern until the selected reserve is reached; per-device sizing hours are intentionally excluded.
Explain what changes the runtime
Runtime moves when available battery energy or average battery-side demand changes. Use the result to identify which measured input would most improve the estimate before changing several assumptions at once.
- Runtime is shorter than required
- Reduce the repeated load, lower the reserve only when acceptable, or compare more nominal capacity after checking output compatibility.
- Runtime looks unusually long
- Check for a measured average that was also given a reduced duty cycle, missing station overhead or an optimistic starting charge.
- An output check fails
- Treat the runtime as unusable for that station until continuous or startup demand fits the corresponding rating.
Before timing a real test
- Charge to the same starting percentage used in the estimate.
- Record the reserve percentage where the test stops.
- Measure the largest uncertain load during representative operation.
- Note ambient temperature and any equipment mode changes.
Method, formulas and verification
Understand the calculation path, the strongest inputs and the limits to verify.
- Battery label
Nominal Wh and capacity retention
- Usable window
Starting charge minus reserve
- Battery demand
Load, conversion loss and overhead
- Runtime
Available Wh divided by average battery W
Enter the battery energy that is actually available
Start with nominal watt-hours, or convert amp-hours using the matching nominal battery voltage. Starting charge, reserve and capacity retention reduce the energy available to the estimate. AC and DC efficiency and station overhead reduce how much of that energy reaches the equipment.
Build a repeating load pattern
A constant device normally uses 100% duty. A cycling device uses running watts during its duty fraction and off-cycle watts for the rest. If you already measured its time-averaged input, enter that average at 100% duty to avoid reducing it twice. Separate rows preserve different models and operating modes.
Interpret runtime with operating limits
The result is the mathematical depletion time for the entered pattern. Real runtime can shift with temperature, battery protection, load-dependent efficiency, aging and changing demand. The output checks still need to cover simultaneous running power and any known startup event.
Available battery energy
Nominal Wh × retention × (start − reserve)Start and reserve are fractions of the retained nominal capacity.
Average battery demand
AC average W ÷ AC efficiency + DC average W ÷ DC efficiency + overheadThe pattern repeats continuously in this view.
Runtime
Available battery Wh ÷ average battery WA zero load has no finite depletion estimate.
What changes the result most?
Change one input at a time and keep the measurement or specification that supports it.
| Input | Effect on the answer | What to verify |
|---|---|---|
| Starting charge and reserve | Define how much retained battery energy is available. | Match the percentages used during the real test. |
| Average load | Higher repeating demand shortens runtime. | Measure changing or cycling equipment over time. |
| AC or DC path | Applies the entered conversion efficiency for that output path. | Choose the port type actually used by the equipment. |
| Station overhead | Matters most when the equipment load is small. | Avoid adding overhead already included in a measured end-to-end value. |
Common terminology
- Runtime
- running time, battery duration, backup time
- Load
- power draw, consumption, demand
- Duty cycle
- cycling percentage, on-time fraction
- Available energy
- usable battery energy, working Wh
Common mistakes
- Reducing a measured average twiceUse a measured time-average at 100% duty unless it represents only the on-state.
- Using amp-hours without voltageAmp-hours convert to watt-hours only with the matching nominal battery voltage.
- Reading runtime as a guaranteeTemperature, battery condition, protection limits and changing loads can alter a physical test.
Watts and watt-hours answer different questions
Watts describe instantaneous power; watt-hours describe energy accumulated over time. Battery capacity and inverter output are separate specifications. A capacity estimate helps with duration, while the output assessment compares demand with entered ratings. Neither establishes connector, voltage, frequency or equipment compatibility. When entering Ah, use the nominal battery voltage associated with that capacity, not the voltage printed next to an AC socket or USB port.
Understand the discharge window
Starting charge and reserve define the fraction of retained nominal battery energy available to this plan. Capacity retention represents the capacity still available relative to the original nominal rating. There is no second depth-of-discharge multiplier: a minimum charge restriction belongs in reserve. Do not enter an already measured usable AC energy figure into the nominal-capacity field and then apply the same conversion losses again. This first release is designed for nominal battery-energy inputs.
Make cycling and standby explicit
Duty cycle is the fraction of the selected operating time spent at running watts. The remaining time uses the entered off-cycle watts. Start with measured values where possible; no refrigerator cycling percentage is inferred just from its name. A row representing measured average watts should normally use a full duty cycle, so the average is not reduced a second time. Output demand assumes rows may overlap unless you explicitly mark equipment Runs separately. Use that setting only when your operating plan prevents it from running with every other row.
Keep startup assessment separate
Enter startup watts per item if known. For rows that may overlap, the tool considers the units within one row starting together while the other rows are already running, then takes the largest row-start event. A row marked Runs separately is checked on its own. Different rows are not assumed to start simultaneously. Missing AC startup values keep the startup result unknown. Even when entered watt ratings cover demand, duration of the surge, apparent power, voltage, frequency, individual ports and protection behaviour need their own equipment-specific check.
Choose assumptions deliberately
AC and DC path efficiencies are editable planning inputs. The initial values are illustrative, not promised performance. The model treats them as conversion efficiencies and adds the separately entered battery-side overhead. Leave overhead at zero if it is already included in an efficiency derived from an end-to-end measurement. Extra capacity margin is reported separately from the base requirement. It changes the sizing recommendation, not the energy consumed by your equipment.
Read runtime as an estimate of a repeating load
Runtime view applies the same repeated duty and standby pattern continuously until reserve is reached. It deliberately does not use the per-row sizing hours, because a schedule with individual stop times would require a different simulation. The Planner shows this runtime estimate alongside its time-limited sizing budget with a separate label. Temperature, varying output efficiency, battery protection and changing equipment demand can shift actual results. A zero load has no finite depletion estimate in this model.
Common battery-runtime examples
Compare steady network, workstation and cycling DC load patterns.
Available energy divided by repeating battery demand
Each scenario first reduces nominal battery capacity by retention, starting charge and reserve. The engine then converts the repeating AC or DC load into battery-side demand before calculating depletion time.
FULL WORKED CALCULATION
Network backup
A 10 W router, 12 W modem and 15 W network switch run continuously from a 500 Wh battery.
- 1Available battery energy
- 2Average battery-side demand
- 3Estimated repeating-load runtime
A small continuous network load can run for many hours, so station overhead and the chosen reserve become material. The runtime answer describes a repeating load and does not reuse per-device hours from a sizing schedule.
Measure the combined router, modem and switch input over normal operation, then confirm the station’s idle demand and AC or DC conversion path.
CALCULATED EXAMPLE 1
Laptop and monitor
A 65 W laptop and 30 W monitor run continuously from a 1,000 Wh battery with a 20% reserve.
- Available battery energy
- 800 Wh
- Average battery demand
- 111.76 W
- Estimated runtime
- 7.16 h
The result is depletion time for a continuous 95 W pattern, not a scheduled workday budget.
CALCULATED EXAMPLE 2
Cycling portable cooler
A 60 W DC cooler runs at 35% duty and draws 3 W off-cycle from a 500 Wh battery.
- Available battery energy
- 450 Wh
- Average battery demand
- 25.5 W
- Estimated runtime
- 17.65 h
The duty and off-cycle inputs form an illustrative repeating pattern; measured averages are preferable when available.
CALCULATED EXAMPLE 3
CPAP battery runtime
A 40 W CPAP load repeats from a 500 Wh battery, starting full and stopping at a 20% reserve.
- Available battery energy
- 400 Wh
- Average battery demand
- 47.45 W
- Estimated runtime
- 8.43 h
Heated humidification and tubing can materially change the measured load.
More common calculations
Calculated by the same engine as the tool.
| Scenario | Entered plan | Calculated answer |
|---|---|---|
| Cycling refrigerator runtime | A 120 W refrigerator repeats at 35% duty with 5 W off-cycle power from a 1,000 Wh battery. | Available battery energy: 850 Wh · Average battery demand: 56.24 W · Estimated runtime: 15.12 h |
| Satellite terminal and laptop runtime | A 75 W satellite internet terminal and 65 W laptop repeat together from a 1,000 Wh station. | Available battery energy: 900 Wh · Average battery demand: 162.09 W · Estimated runtime: 5.55 h |
Calculated reference table
Each row uses a 100–10% battery window, 100% retained capacity, 85% AC efficiency and zero additional station overhead.
| Scenario | Inputs | Engine result |
|---|---|---|
| 500 Wh battery at 50 W | 500 Wh nominal battery; 50 W AC load | Available: 450 WhRuntime: 7.65 h |
| 500 Wh battery at 100 W | 500 Wh nominal battery; 100 W AC load | Available: 450 WhRuntime: 3.83 h |
| 1,000 Wh battery at 100 W | 1,000 Wh nominal battery; 100 W AC load | Available: 900 WhRuntime: 7.65 h |
| 1,000 Wh battery at 300 W | 1,000 Wh nominal battery; 300 W AC load | Available: 900 WhRuntime: 2.55 h |
| 2,000 Wh battery at 500 W | 2,000 Wh nominal battery; 500 W AC load | Available: 1,800 WhRuntime: 3.06 h |
These runtimes describe the entered repeating patterns. Temperature, battery protection, changing loads and real conversion curves can change measured operation.
Battery-runtime questions
Understand repeated loads, amp-hours and the causes of real-world runtime differences.
How long will a 1,000 Wh power station run a 100 W load?
The ideal ten-hour division is reduced by the usable charge window, capacity retention, conversion efficiency and station overhead. Enter those values with the 100 W load to calculate a result that matches the intended operating conditions.
How long can a power station run a refrigerator?
Runtime depends on the refrigerator’s average cycling demand, conversion losses and available battery energy. Use measured average watts at 100% duty, or enter running watts with a representative duty and off-cycle value.
Can a portable power station run a CPAP overnight?
Enter the CPAP’s representative power with the intended humidifier and heated-hose settings. The estimate can compare energy and output, but medical suitability and continuity requirements need confirmation from the device and power-station manufacturers.
Why does runtime view not ask for usage hours?
It estimates how long a repeating load can continue. A schedule where individual devices stop at different times is an energy-budget problem; use the sizing or complete-planner view for that calculation.
Can I estimate battery runtime from amp-hours?
Yes, when you know the nominal voltage associated with that amp-hour capacity. The calculator multiplies amp-hours by nominal volts to obtain watt-hours. Do not use an AC outlet voltage or charger output voltage unless it is the stated basis of the battery rating.
How do two appliances affect battery runtime?
Their battery-side demands are combined when both are active. Separate rows preserve different AC or DC efficiencies, cycling behavior and output checks.
How does reserve percentage affect runtime?
A higher reserve leaves more energy unused and shortens the calculated runtime. Reserve protects the planning window you choose; it should not be confused with a second efficiency loss.
Why is measured runtime different from the estimate?
Check actual average device power, conversion path, idle overhead, starting charge, reserve, temperature and battery condition. A deterministic estimate can only be as representative as those inputs.
Sources, assumptions and model limits
Technical references and what this simplified model leaves out.
Reviewed 6 September 2026. Sources support terminology and methodology, not the illustrative equipment presets or default efficiency values.
- US Department of Energy — Energy Efficiency in the Home
Background on appliance electricity use. Historical educational material, not a current equipment catalogue.
- Victron — Inverter technical specifications
Shows why efficiency, idle demand, temperature and surge duration are separate specifications. Its product values are not universal defaults.
- Jackery — Watt-hour and battery ratings
Reference for energy units and the nominal-voltage requirement when starting from amp-hours. No product recommendation.
This runtime model treats the entered load pattern as repeating and does not predict battery temperature effects, chemistry-specific discharge curves, inverter low-voltage shutdown, changing equipment demand or component ageing. The result is an energy estimate to compare with a representative timed test.