Portable Power Station Sizing
How to Size a Portable Power Station
Zaron calculates energy capacity and AC power output independently, then separately checks startup and voltage. Calculate, don't guess.
Enter your own watts and hours. Zaron does not guess them. Starting example: 100 W for 10 h. 90% efficiency and a 20% margin are Zaron planning assumptions, not universal constants.
Build my full backup planThe core idea
Battery Capacity and AC Output Are Different.
Watts: power at one moment
How much your appliances need right now. This is what the inverter's AC output must cover.
Watt-hours: energy over time
How much the battery must store to run those appliances for the outage. Watts × hours.
You can have enough battery capacity and still fail to run an appliance because the inverter output is too low. Likewise, a unit with high AC output can run out quickly if capacity is too small for your runtime.
≠ 2 kWBATTERY ENERGY vs. POWER OUTPUT
Two Specifications. Two Different Problems.
2 kWh describes how much energy a battery stores. 2 kW describes how much power a system can deliver at once. One decides how long, the other decides whether the load can run at all. Size both.
Illustrative planning scenarios
Quick Sizing Scenarios.
Illustrative categories, not product recommendations. Your loads decide the numbers.
Wi-Fi + phones + lights
Small energy need and a low AC output requirement. Verify chargers and router labels.
Refrigerator + Wi-Fi + lights + electronics
Energy grows with hours; check the refrigerator's startup requirement.
Add a sump pump or furnace blower
Motor loads make startup capability a separate check.
Microwave, kettle, window AC
High watts raise the output requirement, and runtime drains energy quickly.
Several major loads together
May involve 240V, transfer equipment and professional installation.
Reading the spec sheet
What the Power Station Specs Mean.
Specifications vary by manufacturer and model. Always read the documentation for the unit you consider.
Battery capacity
Stored energy. Sets how long loads can run.
Continuous AC output
Power the inverter can deliver steadily.
Surge / peak output
Brief capability for startup; check the documented rating.
AC outlets
Number and type of outlets matter for your plugs.
120V output
Common for portable loads.
240V output
Required by some larger appliances and systems; not all units offer it.
Solar input
Maximum solar charging power; real recharge depends on conditions.
AC charging
Wall recharge capability and speed.
Expansion batteries
Whether the system can add capacity.
Pass-through / UPS features
Model-specific; verify in the manual.
Voltage
Before Buying, Check Voltage.
Many portable power stations provide 120V AC only. Some loads may require 240V, split-phase capability, transfer equipment or dedicated circuits. A high enough watt rating does not mean a battery can power a load.
Read the 120V vs 240V guideRuntime
Estimating Runtime, With the Math Shown.
Approximate runtime hours = usable battery energy ÷ load watts. Real systems have conversion losses and varying loads, so Zaron's recommendation includes an assumed 90% efficiency and a 20% margin.
1.00 ÷ 0.90 × 1.20 = 1.33 kWh recommended planning capacity
2.00 ÷ 0.90 × 1.20 = 2.67 kWh recommended planning capacity
Why nameplate watts matter
Not All Numbers Are Equal.
Never treat a generic internet estimate as an exact specification.
Common sizing mistakes
Six Ways to Size It Wrong.
Buying by kWh alone
Capacity does not tell you whether the unit can output enough watts.
Ignoring inverter output
A big battery with low AC output may not run your load.
Ignoring startup loads
Motors and compressors can need more at startup. Verify specs.
Assuming everything runs continuously
Cycling loads use less energy than their running watts × clock time.
Ignoring 120V vs 240V
A watt rating that fits does not fix a voltage mismatch.
Sizing with zero reserve
Losses and real conditions vary; plan a margin.
Outage duration
Duration Changes the Battery You Need.
Illustration for every 100 W of constant load. You can also reduce duty cycle, sequence loads and prioritize essentials.
| Duration | Raw energy | Recommended (÷ 0.90 × 1.20) |
|---|---|---|
| 4 hours | 0.40 kWh | 0.53 kWh |
| 12 hours | 1.20 kWh | 1.60 kWh |
| 24 hours | 2.40 kWh | 3.20 kWh |
| 72 hours | 7.20 kWh | 9.60 kWh |
Decision framework
Ten Steps Before You Choose a Model.
Not a product roundup. Calculate the requirement first.
Recharging matters
A Power Station Is Not Just a Battery.
In longer outages, charging strategy matters. Do not rely on solar recovery times without model-specific data.
Grid charging
Start full; keep the unit charged.
Solar charging
Recovery depends on panel wattage, weather, sun angle, shading, controller limits and state of charge. No time is promised without model-specific data.
Generator-assisted
Where supported by the model; verify the manual.
Vehicle charging
Where supported by the model; verify the manual.
Methodology
Numbers You Can See. Assumptions You Can Check.
CONTINUOUS W = Σ running W at the same time
90% efficiency and a 20% margin are Zaron planning assumptions, not universal constants. Peak is estimated as the largest entered startup watts plus the other simultaneous running watts.
Evidence / sources
Where the Numbers Come From.
U.S. Department of Energy
Energy Saver guidance on estimating appliance energy use (watts × hours).
ENERGY.GOV →Manuals & spec sheets
Output watts, surge ratings, voltage and charging limits come from the documentation of the specific appliance and power station. Zaron does not supply them.
FAQ
Straight Answers.
What size portable power station do I need?
It depends on two separate numbers: the total watt-hours your loads will consume (battery capacity) and the maximum watts they need at the same time (continuous AC output), plus startup capability for motor loads. Use the sizer on this page to calculate both.
Is a 1 kWh power station enough?
It depends on your loads and runtime. Zaron's planning formula is raw kWh ÷ 0.90 × 1.20. For example, a 100 W load for 10 hours needs about 1.33 kWh of planning capacity, which is already above 1 kWh. Also check that the AC output covers your loads.
Is a 2 kWh power station enough?
It can cover modest loads for a limited time, but it depends on watts, hours, startup needs and voltage. Calculate your own raw energy and apply the planning factors. 2 kWh describes stored energy, not AC output power.
How many watts should my power station have?
Add the running watts of the loads you expect to run at the same time, then check whether any motor loads need startup power above that. Use the label, manual or a watt meter, and verify manufacturer specifications for startup values.
What is the difference between watts and watt-hours?
Watts measure power at one moment. Watt-hours measure energy over time: watts × hours. A power station needs enough output watts to run the loads and enough watt-hours to run them for as long as you need.
How do I size a power station for a refrigerator?
Start from the refrigerator's label (for example annual kWh) or measure with a watt meter, because it cycles on and off. Then verify startup requirements in manufacturer specifications. See Zaron's refrigerator page for the method.
How do I account for appliance surge watts?
Use documented values from the appliance manual or manufacturer, or measured values. Zaron does not guess surge numbers. If none exist, verify manufacturer specifications before choosing a unit.
Can a portable power station run a microwave?
Possibly, if the unit's continuous AC output and surge rating cover the microwave's electrical input requirement and the voltage matches. Check the microwave's label and the power station's specifications.
Can a portable power station run an air conditioner?
It depends on the AC's voltage, running watts, startup demand and your runtime. Many window units are 120V and larger systems are often 240V. Verify the nameplate and manufacturer specifications, and expect high energy use over time.
Do I need 240V backup power?
Only if a load you want to run requires 240V. Many portable power stations provide 120V AC only. Check each load's nameplate and see Zaron's 120V vs 240V guide.
How long will a portable power station last?
Approximate runtime is usable battery energy divided by load watts. Real systems have conversion losses and varying loads, so Zaron uses 90% assumed efficiency and a 20% planning margin. These are planning assumptions, not guarantees.
Should I oversize my battery?
A planning margin is sensible because real loads, losses and conditions vary. Zaron applies a 20% margin, which is a planning assumption, not a rule. Oversizing has cost and weight trade-offs, so size from your own loads.
Don't buy the battery first
Build the Load Plan First.
Size the energy, power, runtime and voltage requirements before choosing a portable power station.
Calculate my full backup plan →