How Many Batteries Do You Need for Your RV or Van?
You need to know how much power you actually use before you can size a battery bank, solar array,
or inverter correctly. Guessing — or just copying "a popular kit" — is how people end up either
overpaying for capacity they don't need, or running out of power on day two of a trip.
This guide walks you through a power audit:
adding up everything you plan to run, so every component you buy matches how you actually live in your rig.
Enter your appliances right in your browser — desktop or phone — and get your recommended
battery bank, solar array, and inverter size instantly. No download, no spreadsheet, and it's
the version we actively maintain, so if we ever fix or improve the math, you get the update automatically.
Prefer to see every line item, tweak the formulas yourself, work offline, or run a 24V/48V system
the calculator doesn't cover? Download the power audit spreadsheet instead — same underlying method, more manual control.
Step 1: Add Each Device
For every device you plan to run, you'll add it to your device list and fill in a few fields.
Here's what each one means:
Field
What to enter
Device Name
Whatever helps you remember it later — "Compressor Fridge," "Laptop Charger"
Watts
The device's max operating wattage (required)
Run Time (Hours)
How many hours per day you expect to use it
Watt Hours (if known)
Optional — if you already know a device's actual daily draw from a meter or spec sheet, enter it here and it overrides the Watts × Run Time math
Duty Cycle
For devices that cycle on and off rather than running continuously — most cycling devices run somewhere between 30–70% of the time
Simultaneous AC Load
Turn this on only for AC devices (running through your inverter) that need to run at the same time as other AC devices — it drives how big your inverter needs to be
12V Fridge
Laptop
Puck Lights
Roof Fan
Microwave
Phone / Camera
The one thing people get wrong on Watts
Some devices look like they plug straight into a normal outlet but are secretly DC devices with a
"wall wart" or power brick inline on the cord — laptops are the classic example. Use the wattage
printed on that brick, not a number you'd guess off the device itself, or your Watts entry
will be wrong from the start.
Step 2: Get Duty Cycle Right for Cycling Devices
Fridges, heaters, and AC units don't run continuously — they cycle on and off to hold a temperature.
Enter their max wattage while running,
then use the Duty Cycle slider to tell the calculator how much of the day they're actually drawing power.
Most cycling devices land between 30–70% duty cycle — if you don't have better data, that's a reasonable starting range to test.
Check the spec sheet first. Some manufacturers publish an average daily draw directly — if so, skip the Watts/Run Time/Duty Cycle math entirely and enter it straight into Watt Hours (if known) instead.
When in doubt, run it high. A duty cycle that's a little too high costs you a slightly oversized system. One that's too low costs you running out of power mid-trip.
Prefer amp-hours and a line-item spreadsheet instead of watts and duty cycle sliders? The power audit spreadsheet comes pre-loaded with benchmark numbers for common devices like fridges and water heaters.
Step 3: Read Your Results
As you add devices, the calculator updates two groups of numbers in real time.
Your power usage
Total Daily Watt HoursYour full day's energy use, added up across every device
Total Daily kWhThe same number, in kWh — useful for comparing against spec sheets
AC Inverting Capacity NeededThe combined wattage of everything you marked as a simultaneous AC load
Solar Wattage GoalSized to replace your daily usage, based on the Peak Sun Hours slider you set for your climate
Recommended system
System Voltage Recommended12V, 24V, or 48V, based on how much simultaneous AC load you need
Minimum Battery Bank SizeSized from your total daily energy use ÷ recommended voltage
Minimum Inverter SizeA specific model recommendation, not just a wattage number
Battery Bank to Support Your InverterSized to the inverter's surge capacity — use whichever of the two battery numbers is larger
A few honest caveats
Solar wattage is based on the Peak Sun Hours you set on the slider — sunny climates run higher, overcast or northern climates run lower. When unsure, set it low; it's safer to oversize your array than come up short.
You'll see two different battery bank recommendations: one from your daily energy use, one to support your inverter's surge capacity. Build to whichever number is bigger — that's the one that actually constrains your system.
These are general recommendations, not a guarantee. Tight budget? Size down, but wire your system so you can expand later without a rebuild.
Got one big single load, like AC or a mini-split? It's usually smarter to run that off a generator rather than size your whole battery bank around it. Try the audit without that item first and see how much smaller your system gets.
Need more than about 16kVA of inverting capacity? The calculator will point you to shop.explorist.life/support instead of guessing at a spec that large.
What's Next
Now that you know your target battery bank size, here's where to go next.
Browse Batteries
See the lithium batteries we stock and support directly — lithium is our standard recommendation for camper builds.
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