Planning your camping power needs starts with a daily watt-hour budget. This simple calculation helps you match your battery or power station to the devices you actually use. By estimating the watt-hours each device consumes per day, you can avoid running out of power or carrying too much weight.

The Formula: Watts Times Hours

Every electrical device has a power rating in watts. Multiply that by the number of hours you run it per day to get watt-hours (Wh). The basic formula is:

Watts × Hours = Watt-hours per day

For example, a fan drawing 10 W for 8 hours uses about 80 Wh. A laptop charger rated at 60 W run for 3 hours uses 180 Wh. Add up the watt-hours for all devices to find your daily energy need.

This number is your starting point. You will then adjust it for inverter losses and add a safety margin. The final daily budget tells you how much battery capacity you need per day, which you can multiply by the number of days between recharges.

Listing Your Devices

Make a list of every device you plan to power while camping. Include the watt rating (usually printed on the device or its power adapter) and an honest estimate of how many hours per day it will run. Common camping devices include:

  • LED lights (5–15 W each)
  • Phone charger (10–20 W)
  • Laptop charger (45–90 W)
  • Portable fan (10–30 W)
  • 12V compressor fridge (often around 40–60 W while the compressor runs, far less averaged over a day)
  • Thermoelectric cooler (runs most of the time, so its daily use is high for the cooling it gives)
  • CPAP machine (30–60 W, depending on humidifier)
  • Small TV or monitor (30–50 W)
  • Camera battery charger (10–20 W)
  • Water pump (20–40 W, used briefly)

If you are unsure about a device’s actual draw, you can measure it with a USB power meter for USB devices or a plug-in watt meter for AC devices. This gives real numbers instead of guesses.

AC versus DC: Adding Inverter Losses

Devices that run on AC (household wall power) must be powered through an inverter when using a battery system. Inverters are not 100% efficient. A common rule of thumb is 85–90% efficiency. To account for this, divide the AC device’s watt-hour total by the inverter efficiency (expressed as a decimal).

For example, if a laptop charger draws 60 W for 3 hours, that is 180 Wh. With an inverter efficiency of 85%, the actual energy drawn from the battery is 180 Wh ÷ 0.85 ≈ 212 Wh. The extra 32 Wh is lost as heat in the inverter.

Devices that run on DC (12V or USB) do not need an inverter. They connect directly to the battery or a USB port, so no conversion loss is added. Examples include 12V refrigerators, USB phone chargers, and 12V LED lights.

When building your budget, separate AC and DC devices. Calculate AC totals and apply the inverter loss, then add DC totals directly.

Example: Minimal Tent Camping

Imagine a minimalist tent camper who uses only a few small devices. The goal is to keep the power station small and light. Devices and estimated usage:

  • Two 5 W LED lanterns run for 4 hours each evening: 2 × 5 W × 4 h = 40 Wh
  • Phone charger (15 W) for 2 hours: 30 Wh (USB, DC)
  • Small fan (10 W) for 6 hours overnight: 60 Wh (USB or 12V, DC)

All devices are DC, so no inverter loss. Total daily need: 40 + 30 + 60 = 130 Wh.

Add a 20% safety margin: 130 Wh × 1.2 = 156 Wh per day. For a two-night trip without recharging, you need 156 Wh × 2 = 312 Wh of usable battery capacity. Most small power stations have a usable capacity around 80–90% of their rated capacity, so you would look for one rated at least 350–400 Wh.

Example: Family Car Camping

A family car camping setup often includes more devices, some AC. Assume they have a medium-sized power station and a small inverter. Devices:

  • LED strip light (10 W) for 5 hours: 50 Wh (DC)
  • Phone chargers (two, 15 W each) for 2 hours: 2 × 15 × 2 = 60 Wh (DC)
  • Laptop charger (60 W) for 3 hours: 180 Wh (AC)
  • Portable fan (20 W) for 8 hours: 160 Wh (DC)
  • Small 12V compressor cooler (50 W while running, about 8 hours of running time a day in warm weather): 50 × 8 = 400 Wh (DC)

DC total: 50 + 60 + 160 + 400 = 670 Wh. AC total: 180 Wh. Apply inverter loss: 180 ÷ 0.85 ≈ 212 Wh. Total daily need: 670 + 212 = 882 Wh. Add 20% margin: 882 × 1.2 ≈ 1,058 Wh per day.

For a three-day trip without recharging, you need 1,058 × 3 = 3,174 Wh of usable capacity. That points toward a larger power station in the 3,500–4,000 Wh range, or you could plan to recharge mid-trip with solar panels. See our camping power station size guide for more on matching capacity to your setup.

Example: Van with a 12V Fridge

A van or RV with a 12V refrigerator is a common scenario. The fridge runs 24 hours a day but cycles on and off. A typical 12V compressor fridge draws roughly 40–60 W while running and runs only part of the time, depending on ambient temperature. For this example, assume 50 W while running and a 40% duty cycle: 50 × 24 × 0.4 = 480 Wh per day for the fridge.

Other devices in the van:

  • LED lights (15 W total) for 6 hours: 90 Wh (DC)
  • Phone and tablet chargers (20 W) for 3 hours: 60 Wh (DC)
  • Laptop charger (60 W) for 2 hours: 120 Wh (AC)
  • Water pump (30 W) used 0.5 hours total: 15 Wh (DC)
  • Vent fan (10 W) for 8 hours: 80 Wh (DC)

DC total (including fridge): 480 + 90 + 60 + 15 + 80 = 725 Wh. AC total: 120 Wh. With inverter loss: 120 ÷ 0.85 ≈ 141 Wh. Total daily need: 725 + 141 = 866 Wh. Add 20% margin: 866 × 1.2 ≈ 1,040 Wh per day.

For a two-day trip without recharging, you need about 1,040 × 2 = 2,080 Wh usable. That calls for a large power station or a dedicated house battery. Many van dwellers combine a lithium battery with solar panels. For detailed advice on fridge power, read running a 12V fridge while camping.

Multi-Day Trips and Recharging

If you are camping for more than one or two days, you will likely need to recharge your battery during the trip. The most common method is solar panels. The daily watt-hour budget tells you how much solar energy you need to replace each day. A general rule of thumb: in full sun, a 100 W solar panel can produce about 300–500 Wh per day, depending on location and season. You can use that to estimate how many panels you need.

For example, the van setup above needs about 1,040 Wh per day. To replace that from solar, you would need roughly 200–350 W of panels in good sun. That assumes you can place them optimally. See our guide on solar panel placement at camp for tips on maximizing output.

Another option is to recharge from your vehicle’s alternator while driving. Charging from a vehicle is slower than the alternator rating suggests: a 12V socket is often fused at around 10–15 A (roughly 120–180 W), while a dedicated DC-DC charger in a van commonly supplies 20–50 A. A few hours of driving still adds useful capacity. If you plan to use this method, factor in your driving time when calculating how many days you can go between full charges.

Remember that usable battery capacity is less than rated capacity. For lead-acid batteries, use only about 50% to avoid damage. For lithium batteries, 80–90% is typical. Always check the manufacturer’s recommendations for depth of discharge.

FAQ

How do I find the watt rating of my device?

Check the device itself or its power adapter. Look for a label that says “Input” or “Power” and lists watts (W). If only volts and amps are given, multiply them: Volts × Amps = Watts. For example, a 12V device drawing 2 A uses 24 W.

Should I include inverter loss for USB chargers?

No. USB chargers that plug into a 12V port or a power station’s USB output are DC devices. They still lose a little energy converting battery voltage to USB or 12V, but usually less than an AC inverter, so your 20% margin generally covers it.

How much margin should I add to my daily budget?

A 20% margin is a common recommendation. This accounts for unexpected extra usage, inefficiencies in wiring, and battery degradation over time. If you know you will be in cold weather, consider a larger margin because batteries lose capacity in low temperatures.

Can I use a power station while it is being charged by solar?

Many power stations support pass-through charging, so you can run devices while solar panels are connected. Some limit output while charging, and charging and discharging at once adds heat, so check the manual for how your model handles it.

Building a daily watt-hour budget takes a few minutes but saves you from guessing and running out of power. Start with your device list, do the math, add inverter losses and a margin, then multiply by the number of days between recharges. The result guides you to the right battery size or solar setup for your next camping trip.