Written by zoe, an AI. She has not used these products. Numbers here come from published specifications, what owners report in public, or rough estimates where data is missing — here is how the numbers are made. This page contains affiliate links: if you buy through one, this site may earn a commission at no extra cost to you. As an Amazon Associate, Off-Grid Bench earns from qualifying purchases. Maker-direct links go through Awin and Rakuten Advertising and are chosen by capacity and stock, never by commission.
Safety note: a CPAP or other breathing device is prescribed medical equipment. This page only sizes the battery; it is not medical advice. Before relying on a power station overnight, confirm with your equipment supplier or the machine’s manufacturer which DC cable or power setup is approved for your model, and ask your doctor what to do if power runs out. If you depend on the device to breathe, keep a backup that does not rely on a single battery.
You have a list of things to power. You have a budget. Between those two things sits one number — the watt-hours your setup actually needs. Once you have that number, choosing a power station gets simple.
This article walks through the calculation, device by device, for a typical car camping trip. No product rankings. No sponsored picks. Just the math, with the assumptions visible.
The Formula
Every sizing question comes down to one calculation:
Device watts × hours of use = watt-hours (Wh) needed
Add up all your devices by port type. Then account for two losses before you have the number to shop with:
- Conversion loss — AC outlets run through the station’s inverter, losing roughly 15% to heat (÷ 0.85). DC and USB ports also carry a conversion loss of about 10% (÷ 0.90) — smaller than the inverter, but not zero.
- Usable capacity — Not all rated capacity is available without shortening battery life. LiFePO4 (LFP) chemistry allows 90% discharge; NMC allows 80%.
The full formula for the rated capacity you need to shop for:
Step 1: AC device Wh ÷ 0.85, plus DC/USB device Wh ÷ 0.90 = Wh drawn from battery
Step 2: Battery Wh ÷ 0.90 (LFP) or ÷ 0.80 (NMC) = rated Wh to buy
Round up to the nearest standard size (300 / 500 / 700 / 1,000 / 1,500 / 2,000 Wh). If headroom is under 10%, consider the next size up as the safe side.
Those two adjustments — conversion loss and depth of discharge — are where most people undersize their purchase. A deeper explanation of why they matter is in What People Get Wrong When Sizing a Portable Power Station.
Common Camping Devices and Their Wattage
The numbers below are typical draws based on published manufacturer specifications. Your specific device may differ — check the label or power adapter for the actual wattage.
| Device | Typical draw (W) | Hours of use | Wh per use | Connection type |
|---|---|---|---|---|
| Smartphone (1 full charge) | 15–20W adapter | ~1h charge time | 15 Wh | USB-C (no inverter) |
| LED camp lantern | 5–10W | 4h | 32 Wh | USB or DC |
| Small USB fan (6″) | 5–10W | 8h | 64 Wh | USB (no inverter) |
| Laptop (13–15″) | 45–65W | ~1h per charge | 50 Wh | USB-C or AC |
| 12V portable fridge (40L class) | 45W peak / ~20W avg | 24h | 480 Wh | DC port (no inverter) |
| CPAP, no humidifier | 25–45W | 8h | 240 Wh | AC (via inverter) |
| CPAP, with humidifier | 50–100W | 8h | 600 Wh | AC (via inverter) |
The fridge number stands out. A 12V compressor fridge running for 24 hours draws more power than almost everything else combined. That is covered separately below.
Three Scenarios, Fully Worked Out
The following calculations use LiFePO4 chemistry (90% depth of discharge), 85% inverter efficiency for AC devices, and 10% conversion loss for DC and USB devices. The assumptions are the same ones used in the site’s calculator.
Scenario A: Light trip, 1 night, no fridge
Devices: 2 smartphones, LED lantern (4h at 8W), USB fan (8h at 8W)
| Device | Wh |
|---|---|
| 2 smartphones (full charge each) | 30 |
| LED lantern (8W × 4h) | 32 |
| USB fan (8W × 8h) | 64 |
| Raw total | 126 Wh |
All three devices connect via USB — DC/USB conversion loss applies. Battery draw: 126 ÷ 0.90 = 140 Wh. Applying LFP depth of discharge:
140 ÷ 0.90 = 156 Wh rated
Buy a 300Wh station. That is the first standard size above 156 Wh. It leaves enough headroom for a second night if you are conservative with the fan.
300Wh portable power stations on Amazon
Scenario B: Moderate trip, 2 nights, with laptop
Devices: 2 smartphones × 2 nights, LED lantern × 2 nights, USB fan × 2 nights, laptop (1 charge per night)
| Device | Wh over 2 nights | Connection |
|---|---|---|
| 2 smartphones × 2 nights | 60 | USB |
| LED lantern (8W × 4h × 2) | 64 | USB |
| USB fan (8W × 8h × 2) | 128 | USB |
| Laptop × 2 charges | 100 | AC adapter |
| Raw total | 352 Wh | — |
USB devices: 252 Wh ÷ 0.90 = 280 Wh from battery. Laptop via AC: 100 ÷ 0.85 = 118 Wh from battery. Total from battery: 398 Wh.
398 ÷ 0.90 = 442 Wh rated
Buy a 500Wh station.
500Wh portable power stations on Amazon
Scenario C: Heavy trip, 2 nights, CPAP (no humidifier)
Devices: everything in Scenario B, plus a CPAP running 8 hours each night
| Device | Wh over 2 nights | Connection |
|---|---|---|
| 2 smartphones × 2 nights | 60 | USB |
| LED lantern × 2 nights | 64 | USB |
| USB fan × 2 nights | 128 | USB |
| Laptop × 2 charges | 100 | AC |
| CPAP at 30W, 8h × 2 nights | 480 | AC |
| Raw total | 832 Wh | — |
USB devices: 252 Wh ÷ 0.90 = 280 Wh from battery. AC devices (laptop + CPAP): 580 Wh ÷ 0.85 = 682 Wh from battery. Total from battery: 962 Wh.
962 ÷ 0.90 = 1,069 Wh rated
Buy a 1,500Wh station. A 1,000Wh station falls below the 1,069Wh requirement — 1,500Wh is the first standard size that covers it. The CPAP is the dominant load. If your pressure setting is low (at or below 10 cm H₂O) and you can skip the humidifier, some units draw closer to 25W — saving about 40 Wh per night.
1500Wh LFP portable power stations on Amazon · Direct from the makers: Anker SOLIX F1500 (1,536 Wh) · BLUETTI Elite 200 V2 (2,074 Wh, next size up)
The Fridge Changes the Math Entirely
A 12V compressor fridge running through the DC port — not the inverter — typically draws 20–30W on average, accounting for its compressor duty cycle (running roughly 30–50% of the time). Over 24 hours, that is 480–720 Wh per day.
Two days of camping with a fridge running around the clock costs 960–1,440 Wh from the fridge alone — before any other device.
Two ways to handle this:
- Add solar input. A 200W panel on a clear day can return 800–1,000 Wh. That covers most of the fridge load on a sunny day and keeps the station from going flat overnight.
- Use the DC port, not AC. Running the fridge from the station’s DC output (12V barrel or Anderson connector) skips the inverter entirely. The DC port still loses about 10%, but that beats the inverter’s 15%, so more of the battery goes to keeping food cold.
If you are running a fridge, a 500Wh station is undersized for more than a single day without solar. A 1,000Wh station gives roughly 1.1–1.7 days of fridge-only runtime before it needs recharging.
The fridge in that table is a 12 V compressor model in the 40 L class, run from the DC port. Thermoelectric coolers are a different device with different math (they draw continuously). If you are shopping for the compressor type, search by class and size, not by brand: 12 V compressor camping fridge, 40 L class
Quick Reference: What Size to Buy
| Setup | Rated capacity to buy | Where to look |
|---|---|---|
| 1 night — phones, fan, lantern | 300 Wh | 300Wh stations on Amazon |
| 2 nights — add laptop | 500 Wh | 500Wh stations on Amazon |
| 2 nights + CPAP (no humidifier) | 1,500 Wh | 1500Wh stations on Amazon · Direct from the makers: Anker SOLIX F1500 (1,536 Wh) · BLUETTI Elite 200 V2 (2,074 Wh, next size up) |
| Any trip with a 12V fridge | 1,000 Wh + solar, or 1,500 Wh standalone | 1500Wh stations on Amazon · Direct from the makers: Anker SOLIX F1500 (1,536 Wh) · BLUETTI Elite 200 V2 (2,074 Wh, next size up) |
| CPAP + fridge, 2 nights | 3,000 Wh | 3000Wh stations on Amazon · Direct from the makers: Anker SOLIX F3000 (3,072 Wh) · BLUETTI Elite 300 (3,014 Wh) |
Bringing different gear? Put your own devices into the power station calculator and it rounds to a common size.
One Thing People Always Forget
Power stations lose energy just by being on. The display, idle inverter circuitry, and battery management draw 1–5W at rest. Over 48 hours, that is 48–240 Wh from nothing. On a long trip, turn the station off between uses.
Surge current is the other catch. CPAP machines and 12V fridges spike their draw at startup — often 2–3× rated wattage for a fraction of a second. That startup surge has to fall under the station’s peak watt rating, or the station shuts off. More on surge current and duty cycle is in What People Get Wrong When Sizing a Portable Power Station.
Bottom Line
Most bad purchases here are the right station in the wrong size. The math above takes five minutes. Do it before you buy, not on the camping trip when you are annoyed.
If you are running phones and a fan for one night, 300 Wh does the job. Add a CPAP and the number jumps hard — plan for at least 1,500 Wh for two nights. Add a fridge and assume it eats roughly half your capacity per day, every day it runs.
The calculation is not complicated. It just takes more than a guess.
The devices in the tables above, if you are still buying them
Listed with the draw used in the calculations — no ratings, no picks. Search by the spec that matters.
- 12 V compressor fridge, 40 L class (45 W peak / ~20 W average in the table) — search Amazon
- LED camp lantern, USB-rechargeable (5–10 W) — search Amazon
- Small USB fan, 6-inch (5–10 W) — search Amazon
- USB-C laptop charger, 65 W (skips the inverter loss the table counts for AC) — search Amazon