How Much Power Do You Actually Need in a Van or RV?

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Almost every question about van and RV power gets asked in the wrong unit. How many days will this last? Is 1,000 watts enough? Do I need two batteries or three? None of those are answerable, because none of them describe what you’re running.

There is one number that makes the whole problem tractable, and it takes about ten minutes to work out for your own trip. Once you have it, the shopping decision answers itself and you stop guessing.

The only math you need

Watts × hours = watt-hours. That’s it.

Watts (W) is the rate something draws power right now. Watt-hours (Wh) is how much energy it consumes over time. A 40 W fan running for 8 hours uses 320 Wh. Batteries and power stations are sold in watt-hours, so if you can add up your loads in watt-hours, you can compare them directly against the thing you’re thinking about buying.

If a spec sheet gives you amps instead of watts, multiply by the voltage: 5 amps at 12 volts is 60 watts. Most 12-volt RV appliances are labelled in amps, so you’ll do this conversion a few times.

Two corrections apply to the raw math, and both push in the same direction:

• Inverter losses. Running a 120 V appliance off a battery means converting DC to AC, which costs roughly 10–15%. Anything you plug into a household outlet should be budgeted about 15% higher than the label says.
• Usable capacity is not nameplate capacity. More on this below, and it’s where most people’s arithmetic quietly breaks.

What things actually cost you

Approximate figures for a night or a day of normal use. Your appliances will differ — this is for getting the shape of the problem, not for final sizing.

Load	Draw	Typical use	Energy
LED lights (whole rig)	5–10 W	5 h evening	30–50 Wh
Phone charging, ×2	—	full charge each	40–60 Wh
Laptop, working	20–45 W	6 h	120–270 Wh
Roof vent fan	12–35 W	8 h overnight	100–280 Wh
12 V compressor fridge	40–60 W cycling	24 h, mild weather	250–450 Wh
12 V compressor fridge	40–60 W cycling	24 h, hot weather	450–700 Wh
Furnace blower (propane heat)	70–120 W	cold night, cycling	150–400 Wh
CPAP, no humidifier	5–15 W	8 h	40–100 Wh
CPAP, heated humidifier + hose	30–60 W	8 h	200–400 Wh
Starlink or similar	40–75 W	10 h	400–750 Wh
Electric kettle	1,200 W	4 min	~80 Wh
Drip coffee maker	900 W	10 min	~150 Wh
Induction burner	1,500 W	20 min	~500 Wh
Rooftop air conditioner	1,300–1,800 W	1 h	1,300–1,800 Wh

Read that table twice and the structure of the problem shows up. Everything electronic — lights, phones, laptops, fans, even a CPAP — is small. The entire top half of the list put together is a few hundred watt-hours. Then heating and cooling appear, and the numbers jump by an order of magnitude.

Heat is the enemy

The dividing line is not “big appliance” versus “small appliance.” It’s whether the device makes heat or moves heat.

Anything with a heating element — kettle, toaster, coffee maker, hair dryer, space heater, induction hob — converts electricity directly into heat, and heat is expensive. Anything that moves heat against a gradient — air conditioner, fridge in hot weather — is running a compressor continuously and is expensive for the same reason.

This is why the standard advice is to keep propane for heating and cooking and reserve electricity for electronics. It isn’t nostalgia for gas appliances. A propane burner and a propane furnace get their energy from a tank you can refill for a few dollars, and they leave your battery to do the job it’s good at: running small loads for a long time.

The corollary is the single most common disappointment in this category: a portable power station will not run a rooftop air conditioner for a meaningful length of time. Even a 2 kWh unit is roughly one hour of air conditioning, assuming its inverter can handle the startup surge at all — most rooftop units pull 2,500–3,500 W for the first second unless a soft-start module has been fitted. Air conditioning genuinely requires shore power or a generator. There is no clever way around it.

What your rig already has

If you’re renting or borrowing, the rig comes with a house battery, and it’s worth knowing what that gives you before you buy anything.

A single 12 V lead-acid house battery rated at 100 amp-hours holds 1,200 Wh on paper. You can only use about half of it. Discharging lead-acid below 50% damages it and sharply shortens its life, so the honest figure is around 600 Wh. Rental fleets and older rigs almost always run lead-acid.

Lithium iron phosphate (LiFePO4) is different: you can use 80–100% of nameplate capacity without harm, so a 100 Ah lithium battery really does give you close to 1,200 Wh. When someone tells you their 100 Ah battery lasts twice as long as yours, this is usually why — not better wiring or a more efficient fridge.

Now put that 600 Wh next to the table above. A cold night with the furnace cycling and a fridge running will consume most of it before morning. That is the entire reason first-time boondockers wake up to a dead battery and a furnace that won’t light: the propane was fine, but the blower needed electricity that wasn’t there.

A worked example

Two people, three nights, no hookups, shoulder season in the mountains. Cold nights, mild days.

Load	Per day
Fridge (mild)	350 Wh
Furnace blower (cold nights)	300 Wh
Roof fan	100 Wh
Lights	40 Wh
Two phones	50 Wh
One laptop, light use	150 Wh
Daily total	990 Wh
Inverter losses on AC loads	~+60 Wh
Realistic daily budget	~1,050 Wh

Three nights is roughly 3,150 Wh with no recharging at all.

The house battery covers about 600 Wh of that. A 1 kWh portable station covers another night. To do the full three nights on stored energy alone you’d need something in the 2.5–3 kWh range, which is heavy and expensive.

The cheaper answer is almost always to put energy back in rather than to carry more of it, which brings us to the part people skip.

Putting energy back

Driving. The most reliable recharge you have, and the one people forget they already own. The engine’s alternator charges the house battery whenever you’re moving. Many portable stations also accept a 12 V input from the cigarette-lighter socket — but that socket is usually fused around 10 A, so you’re getting about 100–120 W. Four hours of driving is under 500 Wh through that route. A proper DC-to-DC charger moves several times that, but it’s an installed component, so it’s not an option in a rental.

Solar. A 100 W panel does not make 100 W. Between imperfect sun angle, heat derating, cloud, and controller losses, a flat-mounted 100 W panel realistically returns 300–500 Wh on a good summer day and can drop to a third of that in winter, under trees, or on an overcast day. Portable folding panels you can aim at the sun do better per watt than a fixed roof panel, at the cost of setting them out and moving them.

So covering the 1,050 Wh daily budget above from solar alone means something like 250–350 W of panel in good conditions, and it means parking in the open rather than in the shade you’d otherwise want. Solar is excellent for stretching a stay from two days to a week. It is not a substitute for having enough capacity to get through a night.

Generators. They work, they’re loud, and a growing number of campgrounds and dispersed areas restrict their hours or ban them entirely. Worth knowing about, rarely worth carrying for a short trip.

Sizing, in plain bands

Once you have a daily watt-hour number, the choice falls out of it. These bands assume a portable power station, since that’s the only option that works in a rental.

Under 500 Wh. Phones, a laptop, lights, a fan for part of the night. Fine for campgrounds with hookups where you just want convenience, or for a single night out. Light enough to carry with one hand.

500 Wh – 1 kWh. One night genuinely off-grid running either a fridge or a CPAP, but not both plus a furnace. This is the size most people should stop at if they camp with hookups nine trips out of ten and go off-grid occasionally.

1–2 kWh. The practical sweet spot for real boondocking. Covers a full day like the worked example above, with enough margin that a cold night doesn’t end the trip. Combined with recharging while you drive, it supports an indefinite loop of drive-a-bit, camp-a-bit. Jackery and EcoFlow both build heavily in this band, and it’s where the useful features — 1,500 W+ inverters, fast solar input, LiFePO4 cells — become standard rather than premium.

Over 2 kWh. Multi-day off-grid without moving, or you’ve decided you want to cook on induction. Be realistic about the weight: units in this class run 20–30 kg (45–65 lb) and stop being something you casually lift in and out of a vehicle. At this point an installed system starts to make more sense — if you own the rig.

Two numbers matter, not one. Capacity in watt-hours tells you how long. Inverter output in watts tells you what you can run at all. A 1 kWh station with a 600 W inverter cannot boil an electric kettle no matter how full it is. Check the continuous output rating against the largest single thing you intend to plug in.

Work out your own number

Print this, walk through the rig, and write the watt-hours next to each item you’ll actually use. Ignore anything you won’t. The total is your daily budget, and everything else is arithmetic from there.

Buying notes that aren’t on the box

Chemistry. LiFePO4 cells are rated for something like 3,000–4,000 charge cycles versus a few hundred for the older NMC lithium used in cheaper units. For a station you cycle every night on a trip, that’s the difference between a decade and a couple of seasons. Most current mid-range models have moved to LiFePO4, but the budget end of the market has not, so check.

Cold. Lithium batteries of any chemistry will not accept a charge below about 0 °C (32 °F) unless the unit has an internal heater. Discharging in the cold is fine. If you’re shoulder-season camping at altitude, keep the station inside overnight and expect slower solar charging on frosty mornings.

Pass-through. Being able to charge the station while things are plugged into it sounds obvious and isn’t universal. It’s what lets you leave it on the 12 V socket while driving with the fridge running off it.

Self-discharge. These units lose charge sitting in a garage. Charge to roughly 60–80% for storage rather than full or empty, and top it up a couple of days before the trip rather than the morning of — some take 6+ hours from a wall outlet.

What not to buy

Don’t buy the biggest unit you can afford on the theory that more is safer. Weight is a real cost in a vehicle with a payload limit, and a 30 kg box you resent moving ends up living in a cupboard at home.

Don’t buy a system that requires installation if you’re renting. You cannot drill, wire, or mount anything in someone else’s rig, and peer-to-peer rental agreements through Outdoorsy and RVshare are explicit about modifications. Portable is not a compromise here — it’s the only category that applies.

And don’t buy anything at all before checking what the rig already has. Some rentals come with lithium house batteries and a solar array on the roof, in which case your power problem may already be solved. Ask the owner for the battery type, the amp-hour rating, and the solar wattage before you shop. Those three numbers take one message to get and can save you several hundred dollars.

The short version

Add up watt-hours for one day. Assume half your lead-acid house battery is usable. Assume a solar panel returns three to five times its wattage over a good day, not eight. Keep heat on propane. Size the inverter for your largest single appliance and the capacity for your night.

Do that and the answer stops being a guess. Most people who go through the exercise end up buying something smaller than they were about to.

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Figures here are typical ranges for planning, not specifications. Check the label on your own appliances and the rating plate on your rig’s battery before committing to a purchase.