A power station that is perfect for charging two phones can be nearly useless beside a camping fridge. The opposite mistake is expensive too: buying a 1,000 Wh battery for one overnight fan means carrying far more weight and cost than the trip requires.
The reliable way to choose a size is to total the energy your own devices will use, account for conversion losses, add a realistic sizing margin, and then check that the inverter can handle the devices running at the same time. This guide uses manufacturer documentation and conservative planning assumptions, not a promise that every power station or appliance performs identically.
Quick answer
For many car-camping trips, these are sensible starting points:
| What you need to power | Capacity class to start with |
|---|---|
| Phones, camera batteries, headlamps, and a small light | A power bank may be enough; otherwise 250-300 Wh |
| The basics plus an overnight USB fan or one laptop charge | 250-500 Wh |
| Two people for a weekend with lights, a fan, phones, and a laptop | About 500 Wh |
| A compressor fridge, CPAP, several people, or multiple nights without recharging | Often 500-1,000+ Wh; calculate the exact load |
Those are shortcuts, not guarantees. A CPAP humidifier, a hot-weather fridge, or an electric cooking appliance can change the answer dramatically. The calculation below takes about five minutes and is more useful than choosing by trip length alone.
Camping power station sizing worksheet
1. List every device and how long it will run
For a device that runs continuously, calculate:
Device energy (Wh) = watts x hours per day x number of days
An 8 W USB fan used for 8 hours on two nights needs:
8 W x 8 hours x 2 nights = 128 Wh
For devices you recharge rather than run continuously, use the battery capacity in watt-hours and multiply it by the number of full charges. A phone battery around 15 Wh charged twice needs about 30 Wh before station and charging losses.
If a battery is labeled only in milliamp-hours, convert it with:
Wh = mAh x battery voltage / 1,000
Use the battery’s stated voltage, not automatically 5 V just because it charges over USB. When possible, use the Wh figure printed on the battery or in the manual.
2. Use daily energy for cycling appliances
A compressor fridge does not draw its rated wattage every minute. It starts, cools the cabinet, switches off, and cycles again. Ambient temperature, ventilation, thermostat setting, food temperature, and how often the lid opens all change the duty cycle.
For a fridge, use a manufacturer figure in Wh per 24 hours or Ah per hour, or measure one full day with the power station display or a watt meter. Do not multiply a 40-90 W compressor rating by 24 hours unless it truly runs continuously.
For the startup checks, daily-energy formula, and 256/512/1,000 Wh examples, use the dedicated camping fridge runtime guide.
3. Account for conversion losses
The capacity printed on a station is nominal battery energy. The device receives less because the inverter, voltage converters, cables, and the station itself consume power.
For an AC-heavy plan, 85% efficiency is a useful conservative estimate:
Conversion-adjusted energy = total device Wh / 0.85
USB and 12 V DC loads can be more efficient because they may avoid the AC inverter. Actual results still vary by model, load size, temperature, and idle time, so 0.85 is a planning assumption rather than a universal specification.
4. Add a sizing margin
Increase the adjusted capacity requirement by 15-25% for colder weather, an extra phone charge, battery aging, longer run time, and estimates that were slightly optimistic. A simple general-purpose worksheet is:
Target station capacity = total device Wh / 0.85 x 1.20
That is roughly the same as multiplying the raw load by 1.4, then rounding up to the next common capacity class.
This formula makes the target capacity 20% larger than the adjusted load. It is not equivalent to stopping with 20% battery remaining; that stricter runtime policy multiplies delivered energy by 0.80. Keep conversion loss and sizing margin conceptually separate, and do not subtract a loss again from a measured outlet-energy result.
5. Check watts as well as watt-hours
Capacity answers how long the station can run. Output wattage answers whether it can run the equipment at all.
Add the wattage of devices that may operate simultaneously and keep that total below the station’s continuous output rating. Fridges, pumps, and other motor loads can need a short startup surge above their running wattage, so check the peak rating too. Kettles, microwaves, induction cookers, and hair dryers commonly demand 700-1,500 W or more; their short runtime does not make them compatible with a small inverter.
Watts, watt-hours, and usable capacity
These three numbers are easy to mix up:
- Watts (W) are the rate of power being used now. A 10 W fan is a small load; a 1,200 W kettle is a large load.
- Watt-hours (Wh) are stored or consumed energy. A 10 W fan running for 8 hours uses 80 Wh.
- Usable capacity is the energy that reaches your gear after conversion and system losses. It is lower than the nominal capacity printed on the case.
A 300 Wh station with 85% delivery efficiency provides about 255 Wh before any planned state-of-charge cutoff. At a constant 10 W load, that is roughly 25 hours in ideal arithmetic. Real runtime may be lower if the AC inverter stays on for a small load, the battery is cold, or the station has meaningful idle draw.
Whenever possible, power USB gear from USB and a 12 V fridge from a compatible DC output. Avoiding the AC inverter can improve runtime, and you can switch the AC section off when it is not needed.
Common camping gear power use
Use this table only for a first draft. The device label, manual, battery Wh rating, or an overnight measurement is better than a generic range.
| Device | Typical planning range | Practical way to estimate it |
|---|---|---|
| Smartphone | 10-20 Wh per full charge | Use the phone battery’s Wh rating; plan near the high end for charging loss |
| Camera battery | 10-20 Wh per full charge | Read the Wh value on the removable battery |
| Laptop | 50-80 Wh per full charge | Use battery capacity, not the charger’s maximum 45-100 W rating |
| LED lantern or string lights | 1-10 W while on | Watts x planned hours; many small camp lights are around 1-5 W |
| USB tent fan | 3-10 W while running | Measure the speed you sleep with; 8 W for 8 hours is 64 Wh |
| CPAP | Often 20-60 W for rough planning | Use the exact model guide or an overnight test; humidifier and heated tubing can raise use substantially |
| 12 V compressor fridge | Often 10-30 W averaged over a stated test cycle | Prefer Wh/24h or Ah/h; running draw may be 40-90 W before cycling is considered |
If overnight airflow is one of your largest loads, first check how to choose a tent fan. Fan size, speed, and placement can reduce the power you need without sacrificing useful airflow.
For medical equipment, do not rely on a generic table or on solar arriving the next day. Follow the device manufacturer’s backup-power guidance, calculate the exact accessories you use, and keep an appropriate backup plan.
Three worked examples
One night with a fan and laptop
Assume one camper brings:
- One phone charge: 15 Wh
- One camera battery: 15 Wh
- A 3 W lantern for 5 hours: 15 Wh
- An 8 W fan for 8 hours: 64 Wh
- One laptop charge: 60 Wh
The raw total is 169 Wh. Adjusting for 85% delivery efficiency gives about 199 Wh. Adding a 20% sizing margin brings the target to about 239 Wh.
Result: choose the 250-300 Wh class. If the laptop stays home, a smaller station or a good USB power bank may cover the remaining load.
Two people for a three-day, two-night weekend
Assume:
- Two phones, one full charge per person per day: 90 Wh total
- One camera battery: 15 Wh
- One laptop charge: 60 Wh
- An 8 W fan for 8 hours on two nights: 128 Wh
- A 3 W light for 4 hours on two nights: 24 Wh
The raw total is 317 Wh. Divide by 0.85 and add a 20% sizing margin:
317 / 0.85 x 1.20 = 448 Wh target capacity
Result: round up to the 500 Wh class. This leaves useful breathing room without jumping straight to a much heavier 1,000 Wh unit.
Two days with a compressor fridge
For a concrete example, Dometic publishes 0.98 Ah/h for its CFX3 35 at 90°F ambient temperature and 39°F inside the fridge. At 12 V, that is about 11.8 W averaged across the cycle, or roughly 283 Wh per 24 hours. Your fridge may use more or less as conditions and usage change.
For 48 hours, the example fridge uses about 566 Wh. Add 60 Wh for phones, 24 Wh for lighting, and 15 Wh for a camera battery. The raw total is 665 Wh.
665 / 0.85 x 1.20 = 939 Wh target capacity
Result: this is already a 1,000 Wh-class trip, with little room for a fan or laptop. Extending the fridge to 72 hours pushes the trip toward 1.5 kWh or more before hot-weather uncertainty. This is why fridge trips should use measured daily consumption instead of a generic wattage claim.
Turn your result into a capacity class
After calculating the final target, map it to a common market size:
| Calculated target | Capacity class to consider | Typical role |
|---|---|---|
| Up to about 250 Wh | 250-300 Wh | Overnight electronics, light, and modest fan use |
| About 251-450 Wh | Around 500 Wh | A comfortable no-fridge weekend for one or two people |
| About 451-850 Wh | Around 1,000 Wh | Longer trips, heavier nighttime loads, or a carefully measured fridge plan |
| Above about 850 Wh | 1,000-2,000+ Wh, or reliable recharging | Fridges, CPAP accessories, groups, and multi-day basecamps |
These boundaries are shopping shortcuts, not physical limits. Choose a station whose rated capacity meets or exceeds your calculated target, then verify continuous output, surge output, port types, weight, and recharge options.
If you are deciding between the common market tiers, compare 300 Wh vs 500 Wh vs 1,000 Wh power stations for camping to see what each step up adds in runtime, weight, output, and recharge needs.
Once you know your capacity class, compare our best portable power stations for camping to see which current model fits it.
How solar charging changes the calculation
Solar panels can replace some of the energy used each day, but their nameplate wattage is not a daily energy guarantee. A useful estimate is:
Daily solar energy = panel watts x peak-sun-hours x 0.6-0.8
For example, a 100 W panel, four peak-sun-hours, and a 0.70 planning factor gives:
100 W x 4 hours x 0.70 = 280 Wh per day
Peak-sun-hours are not the same as total daylight. Cloud, shade, panel angle, temperature, cable loss, and the station’s charge controller all affect the result. The station also has limits for solar input wattage, voltage, current, and open-circuit voltage; the panel configuration must stay within all of them.
For a short trip, treat solar as replenishment rather than permission to buy an undersized battery. Keep enough stored capacity for at least one night without sun, especially when the load is a fridge or medical device. For a location-specific production estimate, tools such as NLR’s PVWatts are more useful than assuming a panel delivers its rating all day.
Once the daily load is known, compare 100 W and 200 W camping solar panels by daily harvest, charging time, portability, and power-station input limits.
Five common sizing mistakes
- Confusing W and Wh. Capacity cannot compensate for an inverter that is too small, and a large inverter does not tell you how long the battery lasts.
- Using maximum wattage as average energy. This badly overstates cycling fridge consumption, while ignoring startup wattage can still make the inverter trip.
- Ignoring conversion and idle losses. Small AC loads can be inefficient when the inverter remains on all night. Use USB or DC outputs when practical.
- Counting ideal solar production as certain. A shaded or cloudy day can remove most of the expected refill.
- Leaving no margin. Cold batteries, aging, changed plans, and one forgotten device turn a perfect spreadsheet into an empty station.
FAQ
Is a 300 Wh power station enough for camping? It often is for one night of phones, lighting, camera charging, and a modest USB fan. Calculate first if you add a laptop, CPAP, fridge, heated gear, or any AC appliance.
How long will a 500 Wh power station run a 10 W fan? At 85% delivery efficiency, the simple estimate is 500 x 0.85 / 10, or about 42 hours. Idle draw, temperature, fan speed, and output path can reduce that number.
Do I need a 1,000 Wh power station for a weekend? Usually not for electronics, lights, and one fan; a calculated 500 Wh class is often enough. A fridge, humidified CPAP, group charging, or electric cooking can make 1,000 Wh reasonable or still insufficient.
How much sizing margin should I add? Start by increasing the adjusted requirement 15-25%. Use more when the weather is cold, appliance consumption is uncertain, the battery is older, or the trip has no dependable way to recharge.
Should I buy a power station just for phones? Usually no. A quality USB power bank is lighter and wastes less energy for phone-only trips. A power station starts to make sense when you need larger total energy, AC power, 12 V output, or several devices.
Sources and measurement notes
- Jackery’s runtime estimate guidance illustrates the common capacity-times-efficiency approach.
- Dometic’s CFX3 35 specifications provide the stated fridge test figure used in the worked example.
- ResMed’s battery guide shows why CPAP model and accessory settings must be calculated specifically.
- NLR’s PVWatts calculator provides location-based solar production estimates.
Specifications and operating conditions can change. Use the label or current manual for your exact device, and measure a real overnight or 24-hour load when failure would matter.
The bottom line
Add the watt-hours your devices will actually consume, divide by a realistic efficiency, increase the result by a 15-25% sizing margin, and round up to the next capacity class. Then make a separate check for continuous and startup wattage.
For a typical no-fridge weekend, that math often lands near 500 Wh. A measured compressor-fridge load can move the same trip to 1,000 Wh or beyond. The right size is not the biggest battery you can afford; it is the smallest capacity that meets the calculation with honest margin.