RV Solar & Battery Calculator — Size Your Off-Grid System

How much battery and solar does your RV actually need? Answer a few plain questions about how you camp — no wattage tables, no amp-hour maths — and this calculator sizes your LiFePO4 battery bank, solar array, inverter, DC-DC charger and MPPT charge controller, using the same method we use to spec systems for travel trailers, motorhomes and off-road campers.

How the sizing works

Three rules drive every off-grid power system: plan around amp-hours per day (not watts on a label), size the battery so your trip fits inside the usable capacity (LiFePO4 gives you 85%+, lead-acid only 50%), and size solar to replace a full day's use in the sun you actually get — not brochure conditions. That's why the calculator applies a 75% harvest derate: controller efficiency, panel temperature, and imperfect sun angles all take their cut.

Frequently asked questions

What if I don't know my power usage?

You don't need to. That's the point of the questions above — answer them the way you'd describe your own camping, and the calculator does the amp-hour maths for you. Open “Where your power goes” in the result to see exactly which number came from which answer.

Can I really run my air conditioner overnight on battery?

Yes, but it is the most expensive answer in RVing, and anyone who tells you otherwise is selling you something. A 13,500 BTU rooftop unit draws around 1,400W while the compressor runs. Eight hours on a warm night is roughly 6kWh — about 500Ah at 12V, before anything else in the rig. That is a serious bank plus the charging to refill it. The honest alternatives are a smaller 12V camping air conditioner, cooling hard before bed and letting it coast, or a generator for the worst nights. The calculator above will show you the real number for your answers rather than a comfortable one.

Portable power station, or a wired system?

It comes down to one number: how many watt-hours you use in a day, and whether a rooftop air conditioner is in the plan. Under about 900Wh a day, a portable station is usually the better buy — no install, no fusing, and you can take it out of the rig. Between 900Wh and 2kWh it still works but you are near the ceiling. Above that, or with a rooftop AC in the mix, a wired bank is the only thing that holds up, because a portable station cannot deliver the sustained current an air conditioner needs. The calculator tells you which side of that line you are on. A useful middle path: a unit like the 2-in-1 PowerMax is a portable station now and a 100Ah house battery when you wire the rig later.

Does a DC-DC charger replace solar?

It replaces some of it, and it works on the days solar doesn't — overcast weather, shaded sites, winter. If you move camp regularly it is often the cheapest amp-hours you can buy, because the alternator is already there. If you park up for a week it does nothing. Most serious builds carry both.

Is this calculator only for Victron gear?

No — the amp-hour and watt math applies to any brand. The main recommendation is Victron because its components integrate into one monitored system and our install guidance covers it. Underneath it you get the same sizing as a Renogy parts list, the lower-cost route most first-time builders take. Not sure which fits? Read Victron vs Renogy.

What if I camp with hookups most of the time?

Size for your longest realistic off-grid stretch, not your average. A system that covers a 2-day boondock handles everything shorter.