How Many Watt-Hours Do You Need for Car Camping? A Real Sizing Method

The most common way people buy power for car camping is also the worst: they pick a brand they have heard of, choose the model that fits the budget, and hope it is enough. Sometimes it is. Often it is either far too small to get through the night or far bigger and heavier than anything they actually run. The fix is not a better brand — it is a better question. Instead of asking which power station to buy, ask how many watt-hours your gear uses in a day, and let that number choose the box.

This is genuinely answerable with grade-school arithmetic. A watt-hour is just watts multiplied by hours, and the capacity printed on every portable power station is measured in exactly those watt-hours. Once you know what each of your devices draws and how long it really runs, you add them up, pad the total for the inevitable losses, and you have the number you should be shopping against. No guessing, no oversized brick of lithium you carry for nothing.

This guide walks the whole method end to end: the three units you need to keep straight, a five-step budget you can do on a napkin, a table of what real camping gear actually draws, why the rated capacity on the box is not the energy you get to use, and three worked profiles from a phone-and-lights minimalist to a full-time rig. By the end you will be able to point at a spec sheet and say that one, because my day is 740 watt-hours — and be right.

Three numbers get tangled together in power-station marketing, and confusing them is where most sizing mistakes start. The first is the watt (W), which is a rate — how fast a device uses energy at this instant. A 50-watt fan uses energy twice as fast as a 25-watt one. Watts are about power, the size of the firehose.

The second is the watt-hour (Wh), which is an amount — power multiplied by time. Run that 50-watt fan for two hours and you have used 100 watt-hours. Watt-hours are about energy, the total water that came out of the hose. This is the unit that matters for sizing a battery, because a power station stores a fixed pool of watt-hours and your job is to make sure your daily draw fits inside that pool. The whole method below is just adding watt-hours.

The third is the amp-hour (Ah), which you will see on 12V batteries and fridge specs. Amp-hours only mean something once you know the voltage, because watt-hours equal amp-hours times volts. A 100 Ah battery at 12 volts holds about 1200 watt-hours; the same 100 Ah label at a different voltage is a different amount of energy. When a fridge says it pulls 3 amps, multiply by 12 volts to get 36 watts before you can compare it to anything. Convert everything to watts and watt-hours first, and the rest of the math stops fighting you. A final habit worth forming: read the device's label, not the marketing page, because the label carries the real rated watts.

Here is the entire method in five steps. Do it once for your kit and you never have to guess at a power station again.

1. List every device you want to run on a typical camping day — fridge, phone, lights, fan, laptop, CPAP, camera batteries, anything that plugs in or charges.
2. Find each device's watts. Read the label or power brick (it lists watts, or volts and amps you multiply together). If you only have amps and it is a 12V device, multiply amps by 12.
3. Estimate the hours it actually runs in a day. Be honest: lights are a few evening hours, a laptop is maybe two, a fridge runs all day but only its compressor cycles (more on that below).
4. Multiply watts by hours for each device to get its watt-hours per day, then add them all up. That sum is your daily energy budget.
5. Scale and pad. Multiply the daily total by how many days you will go between recharges, then add about 20-30 percent for conversion loss, cold, aging, and heavy days. The padded figure is the rated capacity to buy.

A quick worked example makes it concrete. Say your day is a 12V fridge at 480 Wh, three phone charges at 60 Wh total, two hours of laptop at 90 Wh, and an evening of LED lights at 30 Wh. That sums to about 660 watt-hours per day. For a single overnight you could almost squeak by on a 1000 Wh station, but pad it: 660 times 1.3 is about 860 Wh of real demand, so a nominally 1000 Wh unit (delivering ~850 Wh usable) is right at the edge for one night and short for two. That is the kind of clear-eyed answer the budget gives you — and it is why the padding step is not optional.

You will eventually want to read your own labels, but these typical ranges let you build a first draft of a budget today. Treat them as starting points, not gospel — the same category varies a lot by model, which is exactly why a sizing method beats a single magic number.

• 12V compressor fridge — 12-60 W while the compressor runs; roughly 350-600 Wh per day in mild weather, more in heat. Usually your biggest load.
• Smartphone charge — about 15-25 Wh for a full charge.
• Laptop — 30-65 W in use; a full charge is roughly 60-110 Wh.
• LED lantern / string lights — 2-10 W; an evening is often under 50 Wh.
• Portable fan — 2-25 W depending on size; a night on low is 30-150 Wh.
• CPAP (no heated humidifier) — 30-60 W; about 250-480 Wh for an eight-hour night. With the heated humidifier and hose on, plan for 600 Wh or more.
• 12V heated blanket — about 45-55 W; a few hours is 100-200 Wh.
• Electric kettle / induction burner — 600-1500 W but only minutes; a 1000 W kettle for five minutes is about 83 Wh of energy, yet it demands a big inverter.
• Satellite internet (Starlink-class) — 50-75 W continuously; all-day use can add 1000-1800 Wh on its own.
• Camera / drone batteries — 50-100 Wh per battery charged.

Two patterns jump out of that list. First, the small chargers — phones, lights, a camera battery — barely move the needle; you could obsess over them and save nothing. Second, three items dominate everyone's budget: the fridge, anything that makes heat, and anything that runs all day like satellite internet. Get those three right and the rest is rounding. That is also the short answer to which appliances you can run comfortably on a given station: the energy hogs, not the phone, decide it.

For most car campers, the single decision that sets the battery size is whether they run a 12V compressor fridge, because it is the one load that draws power around the clock. But the way it draws is widely misunderstood, and misunderstanding it is how people end up with a battery that dies at 3 a.m. The fridge does not pull its rated wattage continuously. Its compressor switches on to pull the box down to temperature, then switches off and coasts, then switches on again. The fraction of the day the compressor is actually running is the duty cycle, and that fraction is what really determines daily energy use.

That is why you cannot just multiply the fridge's wattage by 24. A unit that draws 45 watts while running but only runs 35 percent of a mild day uses roughly 45 times 24 times 0.35, or about 380 watt-hours — not the 1080 you would get by assuming it never cycles off. The honest way to learn how much a 12V fridge draws for your kit is to watch your own unit over a real day, because duty cycle depends on things no spec sheet can predict.

And those things swing hard. Heat is the big one: a fridge in a hot, sun-baked cabin runs far more of the time than the same fridge in cool shade, so a summer-desert duty cycle can be double a spring-forest one. A lower temperature setting, a packed box opened constantly, poor ventilation around the condenser, and warm food loaded in all push runtime up too. The practical takeaway: budget your fridge on the HOT end of its range if you camp in summer, give it shade and airflow, and treat any quoted daily figure as a mild-weather best case. When the fridge is in your kit, it is the number to nail first; everything else is a footnote next to it.

Here is the trap that catches careful budgeters: you add your watt-hours perfectly, buy a station rated for exactly that, and still come up short. The reason is that the watt-hours printed on the box are the energy stored in the battery, not the energy delivered to your devices. Some of it is lost on the way out.

The biggest loss is the inverter. Turning the battery's DC into the AC that wall-plug devices need is not free — conversion and control overhead typically cost around 15 percent, so a 1000 Wh station commonly delivers closer to 850 Wh to an AC load. The rule of thumb that saves you here: for AC devices, plan on about 85 percent of the rated number being usable. DC and USB loads skip the inverter and lose less, which is a real reason to run a 12V fridge from the station's DC port rather than through the AC outlet on its factory power brick — you keep more of your stored energy.

There is a second number on the box that is not about energy at all, and ignoring it strands people just as often. A station's continuous output rating in watts caps how much power it can deliver at once, regardless of how much energy it stores. A 1000 Wh station rated for 600 watts continuous physically cannot run a 1200-watt kettle, even though it has plenty of stored watt-hours to spare. Motors and compressors add a brief startup surge above their running watts, so the surge rating has to cover the largest motor you start. Always check two things against your gear: enough watt-hours for the day, and enough continuous (and surge) watts for the single hungriest device.

The padding step in the five-step budget is not a fudge factor to feel safe — it is accounting for real physics that quietly shrink your usable energy. The first is temperature. Lithium batteries deliver less of their rated capacity when they are cold, so the same station that comfortably covers your night in mild weather can fall short on a freezing one. Worse, the cold hits from both sides: as the battery gives you less, your fridge runs harder to fight the temperature swings, and a heated blanket or heater you would never use in summer suddenly joins the load list. A winter trip can need substantially more headroom than the identical gear in spring.

Size for the worst night you will actually camp in, not the average one — the battery that is perfect in May is the battery that dies in January.

There is also a hard limit many people meet the cold way: a great many LiFePO4 power stations will not charge below freezing, to protect the cells. They will happily power your gear in the cold, but you cannot solar-recharge them on a frosty morning until they warm up. If you camp in real winter, that turns recharging from a daily refill into a planning problem, which argues for buying extra capacity rather than counting on topping up every day.

The second slow leak is age. Every charge cycle takes a tiny bite out of a battery's capacity, so a station that delivers its full rated watt-hours out of the box will deliver noticeably less after a few hundred cycles. Sizing right to your daily total means the battery is already marginal when new and genuinely too small in two years. The 20-30 percent buffer covers cold, age, conversion loss, and the occasional day you run more than planned — which is why it belongs in the math, not in your optimism.

Numbers land better as people. Here are three common car-camping setups, each budgeted with the method above, so you can find the one closest to yours and start from its total.

• The minimalist (200-400 Wh per day). Phone charges, a couple of LED lights, a small fan, an occasional laptop top-up, no fridge. The whole day might be three phone charges (60 Wh), an evening of lights (30 Wh), a few hours of fan (80 Wh), and a partial laptop charge (70 Wh) — call it 240 Wh. Padded, that is about 310 Wh. A compact station in the 300-500 Wh class covers a weekend easily and recharges fast. This camper is buying convenience, not survival, and should resist the urge to over-buy.
• The weekend camper with a fridge (500-900 Wh per day). Add a 12V fridge to the minimalist and everything changes. Fridge at 480 Wh, plus the same phones, lights, fan, and laptop, lands near 720 Wh per day. Padded, that is roughly 940 Wh, and across a two-night trip with no recharge you are asking for nearly 1900 Wh. This is the sweet spot for a 1000 Wh-class station for a single night, or a 1500-2000 Wh unit (or a 1000 Wh unit plus solar) for a long weekend. The fridge moved this camper up a whole tier.
• The full-timer or remote worker (1500-3000+ Wh per day). Now add satellite internet running much of the day (1200 Wh), heavier laptop use, camera-battery charging, maybe a heated blanket in shoulder season, on top of the fridge. The daily total clears 2000 Wh fast, and a single night of buffer pushes it higher. This setup needs a large bank — 2000 Wh and up — and, just as importantly, a real recharge plan, because no battery this side of a trailer carries several days of that load. Solar and alternator charging stop being nice-to-have and become part of the system.

Everything so far has sized the battery as a closed tank you fill once and drain. In reality you can pour energy back in while you camp, and a steady refill can shrink the battery you need dramatically — a generous recharge source effectively adds watt-hours to your budget every day. There are three common taps, and they are very different in how much they deliver.

• Solar is the camper's favorite because it is silent and needs no fuel, but it delivers far less than its sticker suggests. A 100-watt portable panel does not make 100 watt-hours an hour; after the real-world derating for sun angle, heat, clouds, and wiring losses, a good sunny day realistically returns roughly 300-500 Wh from that panel. If you want to know how long a solar generator takes to refill, that derated daily figure — not the panel's nameplate — is the number to use. Want more daily refill? Add panel watts: a solar panel array of 200 watts roughly doubles the return, weather permitting.
• Charging from the vehicle is the other reliable refill. A basic 12V-socket charge is slow, often capped near 100-120 watts, so a long travel day adds a useful but modest top-up. A dedicated DC-DC charger wired to the alternator can move several hundred watts and genuinely refill a bank between camps, which is why van and overland setups lean on it. Wall charging before you leave is the simplest of all — start every trip full, since the cheapest watt-hour is the one you brought from home. Put a realistic daily refill next to your daily draw, and you may find a smaller, lighter station carries you indefinitely where you assumed you needed a monster.

Pin this somewhere. It is the whole guide compressed into a checklist you can run in ten minutes with your gear in front of you.

• Convert everything to watts first. Volts times amps equals watts; a 12V device's amps times 12 equals watts. Do not compare amp-hours across different voltages.
• Watt-hours per device = watts x hours actually run. For a fridge, multiply by its duty cycle (the fraction of the day the compressor runs), not by a full 24 hours.
• Sum the devices to get your daily watt-hour budget.
• Multiply by days between recharges to get the trip total.
• Add 20-30 percent for inverter loss, cold, aging, and heavy days.
• Divide AC needs by 0.85 (or just shop a rated capacity above your padded number) so usable energy still covers the day after conversion loss.
• Check continuous and surge watts against your single hungriest device — a kettle or induction burner needs a big inverter, not just big storage.
• Subtract a realistic daily recharge (derated solar, DC-DC, or wall) before you leave, since refilling shrinks the battery you must carry.

Run that list and the answer falls out as a single defensible watt-hour figure with a reason attached. Compared against the capacity printed on any spec sheet, it tells you in seconds whether a given station is undersized, right, or overkill for the way you actually camp.

How many watt-hours you need is not a brand question or a gut feeling — it is a sum you can do on the back of a receipt. List your gear, convert each device to watts, multiply by the hours it really runs (duty cycle for the fridge), add it up, scale by your off-grid days, and pad the total for the losses you cannot see. That padded number, checked against both the rated watt-hours and the continuous-watt rating on a spec sheet, is the honest size of the battery you should buy.

For most people the shape of the answer is simple. A phone-and-lights camper lives comfortably in the 300-500 Wh class. Add a 12V fridge and you jump to roughly 1000 Wh, or more for multiple nights without a recharge. Pile on satellite internet, heavy laptop work, and cold-weather heat, and you are into 2000 Wh and beyond with solar as a genuine part of the system. The fridge and anything that makes heat or runs all day are what move you between those tiers; the small chargers barely register.

Do the budget once and the whole anxiety of buying power evaporates. You stop hoping a box is big enough and start knowing it is, because you sized it to your real day with margin for the cold night and the aging battery. That is the difference between carrying a battery and carrying the right battery — and it is worth the ten minutes it takes to find your number.