Most 12V setups fail the same way: someone guesses. They buy a battery that sounded big, a panel that sounded powerful, and find out on night two — fridge warm, lights dim — that the guess was wrong. This 12v camping power calculator replaces the guess with your actual numbers. Enter everything you run at camp, how long you run it, and what battery and solar you have (or are thinking of buying). It works out your daily draw in watt-hours and amp-hours, how many days your battery really lasts, and how much solar you need to replace what you use.
It takes about two minutes, and it is the same maths we walk through in our campsite power audit guide — just without the notebook. If you are still choosing hardware, run a few combinations through the calculator before you spend anything: panel and battery sizes are much cheaper to change on this page than in a shopping cart.
12V Camping Power Calculator
Add your appliances, set your battery and solar, and get your numbers. Everything updates as you type.
Enter what you run each day and the calculator does the rest.
Know Your Numbers? Now Size The Hardware
Pair your result with our tested shortlists — panels that survive Aussie roofs and heat, and power stations that run a fridge overnight without drama.
How This 12V Camping Power Calculator Works
Every figure on this page comes from three sums, and it is worth knowing them because they explain most “my battery died” stories.
Daily draw. Each appliance’s watts × hours run per day × quantity, added together, gives watt-hours per day (Wh). Divide by 12 to get amp-hours (Ah) — the unit batteries are sold in. A fridge is the trap here: it does not run flat-out around the clock, it cycles. If your fridge draws 50W and runs about half the time on a warm day, enter 50W × 12 hours, not 24 — the starting rows above are set up exactly that way.
Usable battery. The number on the battery case is not the number you can use. An AGM or lead-acid battery should only be drained to about 50% if you want it to last more than a season, so a 100Ah AGM gives you roughly 50Ah — 600Wh — of working capacity. A lithium (LiFePO4) battery tolerates deeper use, around 80%, so the same 100Ah delivers about 80Ah (960Wh). That difference, not the sticker, is what you are paying for.
Solar replacement. A panel only produces its rated watts in strong, direct sun for a few hours a day. The calculator multiplies panel watts × your peak sun hours × 0.8 to allow for heat, angle, cable and controller losses — in Australian summer heat, panels routinely lose 15–25% of their rated output, so the 0.8 factor is realistic, not pessimistic. Five peak sun hours is a fair planning figure for much of Australia in the warmer months; use 3–4 for southern winter trips.
A Worked Example: Fridge, Lights And Phones
Take a typical touring setup: a 12V fridge averaging 50W over 12 hours (600Wh), LED lights at 15W for 5 hours (75Wh), two phones charging at 12W for 3 hours (72Wh) and a water pump at 60W for half an hour (30Wh). Daily draw: 777Wh, or about 64.8Ah.
On a 100Ah AGM battery, only 600Wh of that is usable — the setup runs dry partway through day one without charging. Add a 200W panel at 5 sun hours and the same setup generates about 800Wh a day: it covers the 777Wh daily draw with a small surplus, and the battery becomes a buffer for nights and cloudy spells instead of the main supply. Swap the AGM for a 100Ah lithium and usable capacity jumps to 960Wh — over a full day of reserve with no sun at all. That is why the order of upgrades matters: solar first if you are stationary, battery chemistry second.
For the bigger picture on choosing between a battery-based setup and a self-contained unit, our power station vs generator comparison covers the alternatives honestly.
Rules Of Thumb Worth Remembering
- The fridge decides everything. It is usually 60–80% of a camp’s daily draw. Size your system around it, not around your lights.
- Plan for one sunless day. If your usable battery cannot carry a full day’s draw, one overcast day puts you in deficit. Two days of reserve is comfortable touring.
- Panel watts are a midday peak, not an average. A “200W” panel delivering 800Wh across a day is doing well.
- Driving is a charger too. A DC-DC charger feeding 25A while you drive replaces 300Wh per hour of driving — on travel days, that can matter more than solar.
- Re-run the numbers when your kit changes. A diesel heater fan, a Starlink dish or a second fridge changes the picture completely.
Frequently Asked Questions
How many amp-hours do I need for a camping fridge?
Work it out from the fridge, not from a rule of thumb. A typical 40–50L fridge freezer averaging 50W and cycling half the time uses about 600Wh a day — 50Ah at 12V. To run it for two days without charging you need 100Ah of usable capacity: a 200Ah AGM bank or a 120Ah lithium battery, before lights and charging are added.
How much solar do I need to run a fridge while camping?
Divide the fridge’s daily watt-hours by your peak sun hours and the 0.8 loss factor. For a 600Wh-a-day fridge at 5 sun hours: 600 ÷ (5 × 0.8) = 150W of panel as a bare minimum. Most tourers fit 200W so cloudy mornings and winter sun angles do not immediately put them behind.
Why does the calculator only let me use 50% of an AGM battery?
Because regularly draining a lead-acid or AGM battery below about 50% shortens its life dramatically — hundreds of cycles become dozens. Lithium (LiFePO4) chemistry tolerates deep discharge, which is why the calculator allows 80% for lithium. You can drain an AGM further in an emergency; you just pay for it in battery lifespan.
Is a power station better than a battery and solar setup?
It depends on how you camp. A power station bundles battery, charger and inverter in one box — simpler, portable between vehicles, and quick to size using this same calculator (enter its Wh capacity ÷ 12 as the Ah figure). A built 12V system usually delivers more usable capacity per dollar for a dedicated touring vehicle. Our power audit guide walks through both paths.
Planning the whole trip, not just the power? Our camping checklist Australia covers every system in the order you pack them — shelter, sleep, kitchen, safety and the car — with the booking and fire rules that catch first-timers out.