The right size comes from adding up what your gear actually draws in watt-hours over a day, not from how many nights you're camping. A fridge, some lights, a CPAP machine and a laptop have very different appetites, and once you know the daily total you can pick a battery with enough usable capacity to cover it, plus a bit of room for a cloudy day.
Below is a quick way to match your situation to a size, a calculator to run your own numbers, and a worked example showing exactly how the maths behind each pick works.
| What you need | What to look at |
|---|---|
| Weekend trips with lights, phone and laptop, no fridge | BLUETTI AC70P, 864Wh with fast AC top-ups |
| One day of a compressor fridge, CPAP and laptop between charges | BLUETTI AC180P, 1,440Wh with enough continuous watts for fridge start-up |
| Multi-day stays off grid with a fridge, CPAP and tools, little reliable sun | BLUETTI Elite 320, 3,200Wh with wheels for moving it |
Use the calculator below to plug in your own appliances if you want a number specific to your setup.
Power station size calculator
Start from a preset, then tick what you'll run and change the numbers to match your own gear. Watts are on the rating plate or charger.
| Appliance | Qty | Watts | Hours | Wh/day |
|---|
Estimates only. Capacity allows 20% for inverter losses and battery you shouldn't use. Fridge watts are while the compressor runs, and hours are how long it runs in a day, which climbs in hot weather. Check the manufacturer's specs before you buy.
Start with what you actually run, not how many days you're away
Every appliance has a watt-hour cost: the watts it draws, multiplied by the hours you use it. A fridge is the tricky one, because it cycles on and off rather than running flat out all day. Use its compressor run time, not the full 24 hours, or you will badly overestimate.
Here's a realistic day for someone running a 12V compressor fridge, basic lighting, a CPAP overnight and a laptop and phone on top:
| Appliance | Draw | Time | Daily watt-hours |
|---|---|---|---|
| Compressor fridge | 50W when running | 12h compressor run time in a 24h day | 600Wh |
| LED camp lighting | 5W | 4h | 20Wh |
| CPAP, no humidifier | 40W | 8h overnight | 320Wh |
| Laptop charging | 65W | 2h | 130Wh |
| Phone charging | 10W | 2h | 20Wh |
| Total | 1,090Wh |
This assumes a 12V, 40L-class compressor fridge in mild to warm weather, basic LED lighting, a CPAP without a heated humidifier, and two to three hours of screen time on a laptop. Change any of those and the total moves with it. If you want a longer rundown of how watts, amps and hours fit together, our guide on working out amp-hours and runtime covers the formula in more detail.
Add the losses before you pick a number
The 1,090Wh above is what the appliances use, not what you need to pull from the battery. Two things change that number.
First, the fridge and the lights in this example run off the station's 12V DC outlet, which skips the inverter entirely and avoids its losses. The CPAP, laptop and phone charger run through the AC inverter, which typically loses 15 to 25 percent of the energy as heat. Using 20 percent as a working figure, the AC side of the load (320 plus 130 plus 20, or 470Wh) needs 470 / 0.8, about 588Wh pulled from the battery. Add the 620Wh of DC load that skipped the inverter, and the real daily draw on the battery is about 1,208Wh.
Second, you never get the full rated capacity in practice. Standby drain, the battery management system's reserve and the last sliver of charge and discharge curve take roughly another 10 percent off what's usable. Dividing 1,208Wh by 0.9 gives about 1,342Wh of rated capacity needed to cover this exact day without any recharging at all.
Match that number to a size band
Once you have a daily figure, picking a station is mostly about how many days you need it to last between charges, and whether your loads are light or fridge-and-CPAP heavy.
Weekend kit without a fridge
Drop the fridge and CPAP from the example above and keep an esky with ice instead, and a typical day looks more like 20Wh of DC lighting plus 150Wh of AC laptop and phone charging. After the 20 percent inverter loss that AC load needs about 188Wh from the battery, for a daily total of roughly 208Wh, or about 231Wh once you allow for the 10 percent usable capacity loss.
Against an BLUETTI AC70P with 864Wh rated capacity, usable capacity works out to about 778Wh, enough for roughly three nights of this lighter load before you need to plug in again. Its 850W AC input also means a full charge to 80 percent takes about 45 minutes, handy if you're only stopping at a powered site for lunch.
One day of fridge, CPAP and devices
This is exactly the 1,342Wh scenario worked through above, a full day of fridge, lights, CPAP, laptop and phone with no recharging in between. The BLUETTI AC180P's 1,440Wh rated capacity covers that with a modest buffer of roughly 100Wh, enough to stretch the laptop a little longer or cover a quieter start to solar charging the next morning. Its 1,800W continuous output also has the headroom to handle a fridge's start-up surge without strain.
Multiple days without recharging
Run the same 1,208Wh-a-day load for two days without any top-up and the raw draw is 2,416Wh, which after the usable capacity allowance comes to about 2,684Wh of rated capacity needed. Run the numbers the other way for the BLUETTI Elite 320: its 3,200Wh rated capacity gives about 2,880Wh usable, which covers roughly two full days of this load before you need mains power, solar or a generator, with some charge left over for a shorter third day if you trim the laptop time.
That makes it a better match for remote stays, hunting camps or stretches of unreliable sun where recharging isn't guaranteed daily. If you're setting up for longer off-grid stretches generally, our guide to going off the power grid covers solar input and site setup alongside battery sizing.
Comparing the three side by side
| Model | Rated capacity | Continuous output | Lifting mode / surge | AC-only charge, 0 to 80% | Weight |
|---|---|---|---|---|---|
| BLUETTI AC70P | 864Wh | 1,000W | 2,000W Power Lifting Mode, resistive loads only | About 45 minutes on 850W AC | 10.7kg |
| BLUETTI AC180P | 1,440Wh | 1,800W | 2,700W Power Lifting Mode, resistive loads only | About 45 minutes on 1,440W AC | 16kg |
| BLUETTI Elite 320 | 3,200Wh | 1,800W | 2,700W Power Lifting Mode, plus 3,600W surge for motor start-up | About 2 hours on 1,440W AC | 34kg |
Power Lifting Mode lowers the output voltage to let resistive heating appliances like kettles, hair dryers and heaters draw above the rated output. It isn't extra continuous capacity and it doesn't suit motors, compressors or sensitive electronics, so size your fridge and CPAP loads against the continuous output figure, not the lifting figure. The Elite 320 separately lists a true surge rating for the brief current spike a motor draws at start-up.
Notice the AC180P charges to 80 percent in the same 45 minutes as the smaller AC70P, despite holding 576Wh more. That comes down to its higher 1,440W turbo input rather than any trick with the battery itself.
Frequently asked questions
How many watt-hours does a camping fridge use a day?
It depends on compressor run time, ambient temperature and insulation, not just the fridge's wattage. A 50W compressor fridge running for around 12 hours in a 24-hour period draws roughly 600Wh, but a hot vehicle or a poorly sealed lid will push that higher.
Can I run a CPAP machine on a portable power station overnight?
Most CPAP machines run fine from a station's AC outlet, and the load in our example above (40W without a humidifier, over 8 hours) is modest. Always check your machine's label for its actual wattage and whether a heated humidifier is fitted, since that adds significant draw, and follow the manufacturer's manual for any medical device you're running off battery power.
Does adding solar panels change what size I need?
Solar lets you top up during daylight, which can mean you don't need to size purely around worst-case multi-day autonomy. But overnight loads like a CPAP or a fridge running through the dark still have to come from stored capacity, so size the battery for your daily load first and treat solar as the refill method, not a substitute for capacity.
What's the difference between Power Lifting Mode and surge?
Power Lifting Mode drops the output voltage to run resistive heating appliances like kettles and heaters above the unit's rated wattage, and it isn't suitable for motors or compressors. Surge is a brief, automatic peak the inverter allows for a motor's start-up current, after which output settles back to the continuous rating.
Still not sure which one suits you?
Get in touch and tell us what you run and where you go. We can talk through your fridge, CPAP or tool list against the numbers above, or you can browse the full Portable Power range to compare capacities side by side.
