Your 4-Hour Outage
Backup Plan.
Keep essential connections, lighting and selected devices running. Build the load list first. Then choose the battery and inverter that can support it.
4-HOUR BACKUP PLANNER
All starting values are illustrative planning placeholders. Replace them with measured or manufacturer data. Run hours mean actual equivalent operating time within this four-hour window.
Battery = raw kWh ÷ 0.90 × 1.20.
90% assumed efficiency + 20% planning margin. No recharge assumed; usable output varies.
Router, LED lights, phone charging and two hours of laptop use. Battery target after efficiency and margin.
Add 150 W × 1.33 equivalent run hours. This duty-cycle example is not a specification for your refrigerator.
Stored energy determines runtime. Continuous and startup power determine whether the system can run the loads.
Four Hours. A Focused Load List.
Stay reachable.
Plan for phone charging and the modem/router. Powering your router does not guarantee that the internet provider will remain online.
Light the rooms you use.
Select a small number of LED lights. Use measured total watts for the lights connected to the battery.
Keep the useful work going.
Include a laptop, fan or other priority device only for the hours it will operate. Add unlisted loads in the Full Calculator.
Keep the Door Closed.
Plan Beyond the Estimate.
FDA guidance says an unopened refrigerator keeps food cold for about four hours. That is a general food-safety guideline, not a guarantee that every outage or appliance is safe.
Use an appliance thermometer and follow FDA guidance when the duration or temperature is uncertain. Include refrigeration backup when your situation requires it, and verify both energy use and compressor startup capability.
Read FDA food-safety guidance ↗Power Essentials.
Preserve Your Reserve.
High-power heat changes the equation.
An illustrative 1,500 W heater running for four hours needs 6 kWh before losses, or an 8 kWh battery target with this method. Compare that with 0.39 kWh for the essentials example. Actual heater watts must be verified.
Know What to Do Before the Lights Go Out.
Charge. Label. Test.
Charge the battery according to its instructions. Label priority connections and test the actual devices together, including startup. Keep a flashlight ready.
Connect the essentials.
Check outage updates. Keep refrigerator doors shut. Use approved connections and monitor battery state while operating only the selected loads.
Protect the remaining energy.
If restoration is uncertain, reduce optional use and prepare a longer plan. Monitor food temperature and maintain a separate plan for medically essential equipment.
The Math, Visible.
Recommended battery = 0.29 ÷ 0.90 × 1.20 = 0.387 kWh ≈ 0.39 kWh
These efficiency and margin values are planning assumptions, not universal constants. Cold temperatures, inverter standby draw, battery aging and device behavior may change actual runtime. Equivalent run hours already account for cycling; do not apply a second duty-cycle reduction.
Capacity Alone Is Not Enough.
Check the inverter.
The calculator sums selected operating watts as a conservative overlapping-load check. Confirm the output rating and all loads that could run together.
Use verified peak data.
No startup watts are invented here. Enter a verified total peak requirement including other loads that remain on. Check supported peak duration with the manufacturer.
Match voltage and outlets.
Verify output voltage, connector and equipment compatibility. Household circuits need an appropriate professionally installed transfer arrangement; never backfeed an outlet.
Evidence Where It Matters.
The four-hour refrigerator guideline.
Food handling and temperature guidance during an outage.
If a generator is part of your plan.
Operate fuel-powered generators outdoors only, at least 20 feet from homes, with exhaust directed away. Follow CPSC guidance and the product instructions.
Examples are transparent.
Device watts and runtimes are editable placeholders. The 90% efficiency and 20% margin are Zaron planning assumptions, not FDA or CPSC recommendations.
Straight Answers.
Is a 500 Wh battery enough for four hours?
It exceeds the 387 Wh capacity target for the essentials example shown here. That does not establish compatibility: check usable capacity, continuous watts, startup capability and actual device draw. With the refrigerator example, the target rises to about 653 Wh.
Do I need to power my refrigerator immediately?
FDA gives a general guideline of about four hours for an unopened refrigerator. Use temperature measurements and the official food-safety guidance. Outages can last longer than expected, so keep a refrigeration or food-storage contingency ready.
Why are refrigerator run hours lower than four?
A refrigerator cycles. The example uses 1.33 equivalent operating hours at 150 W across the four-hour window. That is an illustrative assumption. Replace it with your measured energy, documented duty cycle or an estimate based on your own EnergyGuide data.
Can this plan cover medical equipment?
This generic planner is not a medical backup assessment. Follow your equipment supplier and care team's continuity plan, including approved backup power, required runtime and an emergency alternative.
What if the outage lasts longer?
Recalculate for the longer duration and reassess essential loads. This four-hour tool does not include solar input or other recharge. Use the Full Backup Calculator for additional loads and longer runtime.