RV Boondocking Power Calculator (Daily Amp-Hours, Battery Days, Solar & Generator Hours)
Add up an RV's 12 V loads off-grid — furnace blower, 12 V fridge or propane fridge control board, water pump, lights, fans, inverter loads and device charging — against usable battery capacity to see how many days you can boondock, what your solar covers, and the generator hours per day to break even.
How it works
daily Ah = furnace hours × 8.5 A + fridge + lights + pump/parasitic + inverter Wh ÷ 12 ÷ 0.85 + devices · usable = bank × (0.50 flooded / 0.55 AGM / 0.85 LiFePO₄) · solar Ah ≈ W × sun-hours × 0.7 ÷ 12.8 · days = usable ÷ (daily − solar × efficiency) · generator h = deficit ÷ (charger A × efficiency × acceptance)
Off-grid an RV lives on its house batteries, and the arithmetic is consumption versus recharge. The furnace blower is the surprise: 8–10 amps whenever it runs, so a cold night can use more power than everything else combined. Lead-acid banks give up only half their rated capacity, solar panels deliver well under their rating on a roof, and stock converters charge slowly — which is why the answer for many rigs is "about two days". This calculator shows where the amp-hours go and how much solar, battery or generator time closes the gap.
Worked example
A trailer with 200 Ah of flooded batteries (100 Ah usable), a propane fridge, 4 hours of furnace (34 Ah), lights, pump and parasitic loads (20 Ah), 400 Wh of inverter use (39 Ah) and device charging (6 Ah) uses about 105 Ah a day. A 200 W panel at 4.5 sun-hours returns about 49 Ah, leaving a 62 Ah deficit — about 1.6 days off-grid, or 1 day with no sun — and roughly 2.1 hours of generator a day through a 45 A converter to break even; about 500 W of solar would cover the load.
Frequently asked questions
How much power does an RV furnace use?
The propane does the heating but the blower motor draws 7–10 A at 12 V whenever it runs. At 30–50% duty on a cold night that is 30–60 Ah — often the whole usable capacity of a single battery. Vent-free propane heaters (with a CO alarm and ventilation) or a diesel heater use a fraction.
Why does my battery die overnight when I only used the lights?
Parasitic loads (detectors, control boards, stereo memory, an inverter left on) add up to 10–30 Ah a day, and a lead-acid battery labelled 100 Ah has only 50 Ah usable — often less if it is old or was never fully charged. Measure with a shunt monitor to see the real draw.
Is lithium worth it for boondocking?
A 100 Ah LiFePO₄ gives 85 Ah usable versus 50 from a 100 Ah lead battery, weighs a third as much, charges 2–3× faster and lasts 3,000+ cycles; you need a lithium-capable converter and, for cold climates, a heated battery or charge cutoff. For people who camp off-grid regularly it usually pays back in generator fuel and battery replacements.
Related calculators
RV figures are planning estimates. Your coach's data plates (GVWR, GAWR, OCCC), tyre load-inflation tables and appliance ratings govern; weigh the rig loaded at a CAT scale and adjust.