The most common camp power failure looks like this: someone buys a 100-watt folding solar panel, leans it against a tire, plugs it into a battery box, and expects it to run a 12V fridge indefinitely. Three days later the fridge is warm, the battery is at 11.4 volts, and the panel gets blamed. The panel was never the problem. The system was sized by vibes instead of arithmetic, and the arithmetic here is not hard.
Camp power is one of the few parts of building a rig where you can predict the outcome before you spend the money. You can't calculate how a shock will feel on washboard, but you can absolutely calculate whether a battery will make it to Sunday.
Start with the load, not the battery
Everyone shops for the battery first. That's backwards. You can't size a bank until you know what it has to feed, and the number that matters is watt-hours per day.
Watt-hours is just volts times amp-hours — a 100Ah battery at 12V nominal holds roughly 1,280 Wh on paper. Working in watt-hours rather than amp-hours saves headaches the moment you mix 12V and 120V gear, because a power station rated in Wh and a battery rated in Ah stop being apples and oranges.
Rough daily draws for typical camp loads:
- 12V compressor fridge, 40-50 quart: the big one. Realistically 300-600 Wh per day depending on ambient temperature, how full it is, how often you open it, and how well it's insulated. In a hot desert with the lid opening every twenty minutes, the top of that range is optimistic.
- LED camp and awning lighting: small. A few tens of watt-hours a night. Not worth worrying about.
- Phones, headlamps, GPS, radios: 50-100 Wh per day for a couple of people. Laptop and camera batteries add 60-150 Wh if you're actually working out there.
- Air compressor: big instantaneous draw, tiny daily total. It matters for wire and fuse sizing, not for bank capacity.
- Inverter running a kettle, induction burner, or hair dryer: the budget killer. A 1,500W appliance for ten minutes is 250 Wh, and the inverter loses another 10-15% as heat.
Add up your real list. Most people who think they need a huge system are actually running a fridge, some lights, and phone charging — call it 500-800 Wh per day. Some genuinely need three times that. The point is to know which one you are before you buy.
Fridge duty cycle is the number people get wrong
A fridge's compressor draws somewhere in the neighborhood of 45-55 watts while running. Multiply that by 24 hours and you get a terrifying number; assume it runs 20% of the time and you get a comfortable one. Reality moves between those poles based on conditions you control.
A fridge parked in direct sun on a black tonneau cover, with the condenser vent pressed against a drawer, will run nearly continuously. The same fridge in shade, with airflow around the vents, full of already-cold contents, might cycle a third as much. Pre-chill everything at home on shore power, fill the empty space — a full fridge holds cold far better than a half-empty one — and give the condenser room to breathe. An insulated cover helps more than most parts you could buy.
Usable capacity is not rated capacity
This is where lead-acid and lithium genuinely diverge, and it's the difference that justifies the price gap.
Lead-acid and AGM can be discharged to about 50% before you meaningfully shorten their life, so a 100Ah AGM gives you roughly 600 usable watt-hours. They also sag under load, so your fridge's low-voltage cutoff may trip before the battery is technically empty. Heavy, cheap, and tolerant of cold.
LiFePO4 runs to 80-90% depth of discharge without drama. A 100Ah LiFePO4 gives you roughly 1,000-1,150 usable watt-hours — nearly double the AGM — at about half the weight. Voltage stays nearly flat until it's nearly empty, so appliances behave predictably, and it charges much faster, which matters when your charging window is a two-hour drive between camps.
The catch: most LiFePO4 cells should not be charged below freezing. Discharging cold is fine; charging cold plates the lithium and permanently damages the cell. Any decent battery has a BMS that blocks charging below roughly 32°F, and better ones include internal heaters. If you camp in the snow, buy the heated version or accept that your solar does nothing until the battery warms up.
You can compare chemistries and capacities in our solar and battery banks collection.
Power station vs. built-in system
There are two legitimate architectures and a lot of tribalism about which is correct. Both work.
The portable power station
An all-in-one box: battery, inverter, MPPT controller, DC outputs, USB, display. You buy one thing, plug things into it, and it works.
The advantages are real. Nothing gets wired into your truck, so nothing gets cut out when you sell it. It comes inside at night, goes in the house during a power outage, and moves to another vehicle. The display tells you exactly what's going in and out, which teaches you your own consumption faster than any spreadsheet.
The costs are real too. You pay a premium per watt-hour for the packaging, and charging from the vehicle usually happens through a cigarette-lighter-style socket limited to roughly 8-10 amps — glacial, maybe 100-120 Wh per hour of driving. Some newer units accept a proper high-current alternator input; those are worth seeking out.
The built-in dual battery or house battery system
A second battery mounted under the hood, in the bed, or in a cargo area, charged by a DC-DC charger from the alternator and optionally by solar, feeding a fused distribution panel.
It's cheaper per watt-hour, it charges fast off the alternator, it's out of the way, and it scales — you add capacity without buying a whole new appliance. It's also a project: heavy cable, a mounting location that survives washboard, fuses at both ends of every run. If you've never done automotive wiring, budget more time than you think and read our breakdown of dual battery systems before you order parts.
A reasonable middle path: a modest house battery with a DC-DC charger for the fridge and lights, and no inverter at all. Most camp loads are natively 12V, and the inverter is usually there for one appliance somebody could live without.
What a solar panel actually delivers
Panels are rated in watts under laboratory conditions: a specific light intensity, a specific cell temperature, panel pointed straight at the source. Your panel is on a roof rack at whatever angle the rack happens to be, in real air, getting hot.
The working rule of thumb is rated wattage times roughly 3 to 5 hours per day in usable summer conditions, and considerably less in winter, in trees, or at high latitude. So a 100W panel is a 300-500 Wh/day panel in good conditions and a 150 Wh/day panel in October under partial canopy. Compare that to your load number. If you're pulling 600 Wh a day on 100 watts of fixed roof panel, you're running a slow deficit and the battery is a countdown timer, not a buffer.
Things that matter more than brand:
- Shade is not proportional. Because cells are wired in series, one shaded cell drops output far more than the shaded fraction suggests. Parking in shade for comfort and expecting full solar output is a contradiction, and it's the biggest reason real-world output disappoints.
- Angle matters, and roof panels are always at the wrong one. A fixed flat panel on a rack is convenient and permanently compromised. A portable folding panel you can aim and move as the sun tracks will beat a larger fixed panel on a lot of days. Many people run both.
- MPPT over PWM. An MPPT controller extracts meaningfully more energy from the same panel, especially in cold and in low light. The price difference is small enough now that PWM is hard to justify.
- Heat cuts output. Panels lose efficiency as they warm up, so build an airgap under any roof-mounted panel.
Panels, controllers, and mounting hardware are in the electrical accessories and solar collections.
The alternator is your real charger
Here's the thing solar marketing doesn't emphasize: if you drive between camps, your alternator is by far your largest energy source. A DC-DC charger pulling 25-40 amps replaces 350-550 Wh per hour of driving. That is one to two entire days of fridge consumption per hour behind the wheel. A day of good sun on a 100W panel doesn't come close.
Solar's real job for most people is holding the system steady on the days you don't move. That's valuable. It just isn't the primary charging source that build threads make it look like.
Two reasons to use a proper DC-DC charger rather than a simple isolator or relay:
- Charge profile. A lithium house battery and a lead-acid starter battery want completely different charging voltages. Tying them together with a relay means one of them is always charged wrong.
- Smart alternators. Many modern vehicles vary alternator output for fuel economy and drop voltage low enough that a passive isolator barely charges at all. A DC-DC charger boosts whatever it's given up to the correct target — and limits current draw, which a lithium battery on a plain relay will happily exceed at the alternator's expense.
Wiring mistakes that cost people batteries
The electrical side is where an otherwise good build turns into a warranty argument or a fire.
- Undersized cable. A long run of thin wire to a DC-DC charger means the charger never sees the voltage it needs and never reaches full output. Size for the round-trip distance, not one-way, and err heavy.
- Fusing only one end. Every conductor gets a fuse within a few inches of the power source it connects to. A battery-to-battery run needs a fuse at both batteries, because both ends are sources.
- Grounding to painted sheet metal. Paint is an insulator. Grind to bare metal, use a star washer, seal it afterward. Bad grounds cause symptoms that look like a dozen other problems.
- No chafe protection. Grommets through sheet metal, loom along frame rails, secured every foot or so. A rig that flexes will find any wire you left loose.
- Mounting a battery to a floor that isn't structural. A 60-pound battery is a projectile in a rollover. Through-bolt to structure with backing plates.
Three systems that actually make sense
Weekend trips, fridge and phones, you drive most days. A 500-800 Wh power station or a single 100Ah battery, charged mainly by a 20-30A DC-DC charger, with a 100W portable panel as insurance. Honestly, this covers most people.
Week-long trips, basecamp for two or three days at a time. 100-200Ah of LiFePO4, a 30-40A DC-DC charger, and 200W or more of solar, ideally split between fixed and portable. Add an inverter only if you have a specific appliance in mind.
Extended remote travel or working from the truck. 200Ah-plus, 300W-plus of solar, and a shunt-based battery monitor. Voltage is a terrible fuel gauge on lithium because the curve is nearly flat across the usable range; a shunt counts amp-hours in and out and tells you the truth. It's an inexpensive part and the best diagnostic you have when something draws more than you expect.
The short version
- Add up your daily watt-hours before shopping for anything.
- Usable capacity is about half of rated on AGM, about 85% on LiFePO4.
- A 100W panel is a 300-500 Wh/day panel in good conditions and much less in shade or winter.
- Your alternator, through a DC-DC charger, out-produces your solar by a wide margin if you drive at all.
- Fuse both ends, size cable generously, and mount the battery to structure.
- Manage the fridge — shade, airflow, pre-chilled and full — and you cut the biggest load substantially for free.
Do the arithmetic once and the rest of the decisions make themselves. Ready to build it? Start with the solar panels and battery banks, then sort out charging and distribution in electrical accessories. More camp-setup guides live in the Overland blog.