Before the Battery

Evidence page

Portable power station for a travel trailer

Short answer: for a dry-camping weekend in a travel trailer, plan on roughly 400–1,200 Wh per night with the fridge on propane, and 1,000–2,000 Wh per night with a 12 V compressor fridge. A 1,000–2,000 Wh station covers that. Roof air conditioning does not fit, at any portable size.

A camper van parked off-grid at dusk with its interior lit and no shore-power post.
The situation this guide sizes: an evening at a campsite with no shore power.

Published 8 August 2026 · Last reviewed 10 August 2026

By Alexis Marchais, engineer and independent decision-system builder.

How this guide calculates

Stored capacity needed = nightly Wh × nights ÷ 0.765. Roof air conditioning is excluded from portable sizing and escalated instead.

Observed / model inputs

  • Declared per-night loads in Wh for the fridge, pump, lights and devices actually taken on the trip.
  • Shore power availability, and the TT-30 connector arithmetic where a pedestal is used: 120 V × 30 A = 3,600 W nameplate.
  • Realistic daily solar yield for the location and season, rather than panel nameplate watts.

Before the Battery planning assumptions

  • 85% AC delivery and a 10% retained reserve, giving the 0.765 planning factor used in the worked example.
  • 2,880 W is used as a conservative in-house ceiling on a TT-30 pedestal, not a universal code limit.
  • Tow-vehicle 7-pin charging is treated as negligible unless charging watts and driving hours are declared.

What makes a travel trailer different

  • No engine, so no alternator of its own. Charging while driving depends on the tow vehicle’s 7-pin circuit, which is typically a trickle, not a charge.
  • Often no installed inverter, so the 120 V outlets are dead unless shore power or a portable station feeds them.
  • A propane absorption fridge draws almost nothing electrically. A 12 V compressor fridge is usually the largest single load of the trip.

A worked two-night example

  • 12 V compressor fridge: 500 Wh/day × 2 = 1,000 Wh.
  • Lights, pump, fans: 150 Wh/day × 2 = 300 Wh.
  • Devices and a CPAP without humidifier: 250 Wh/day × 2 = 500 Wh.
  • Total at the outlet: 1,800 Wh.
  • After an 85% delivery factor and a 10% retained reserve (conservative Before the Battery planning assumptions): about 2,350 Wh stored.

So the honest answer for that trip is a 2,000 Wh class station plus meaningful solar, or one shorter night, or the propane fridge. A single 1,000 Wh unit does not close it.

Where it stops working

Roof air conditioning, electric water heating and residential microwaves are shore-power or generator loads. If the plan requires them off-grid, the correct verdict is a different architecture — an installed lithium bank with a large inverter, or a generator — not a larger portable box.

Decision case RV-02 works that boundary through on a TT-30 trailer, and decision case RV-01 shows the same method on a weekend that does close.

Check your own trip

Run the RV weekend check. It starts with shore power availability and the battery you already own, and it abstains when air conditioning is requested without a provable supply. See also the general RV guide, the published RV sizing method and the decision case index.

Reproducible dataset

The refrigerator portion of a dry-camping weekend can be checked against a published dataset rather than a rule of thumb.

Refrigerator outage sizing table: 15 transparent scenarios — formula, assumptions, gate states, XLSX and CSV.

Primary sources

Merchant marketing is never used as a primary source for generic arithmetic. Specific product or model specifications still require dated OEM documentation plus independent measured evidence.

  1. 30 amp general electrical information (RV shore power)Heartland Owners technical reference

    Supports: The TT-30 connector arithmetic: 120 V × 30 A = 3,600 W nameplate.

    Manufacturer/owner technical reference, not a government source. Used only for the connector arithmetic.

  2. PVWatts CalculatorUS National Renewable Energy Laboratory

    Supports: That realistic daily solar yield is location- and season-dependent, and must be estimated rather than assumed from panel nameplate watts.

  3. Keep your food safe during emergenciesUSDA Food Safety and Inspection Service

    Supports: The food-safety holding times that make refrigerator and freezer backup a time-bounded problem rather than an open-ended one.

Browse all guides, diagnostics and research — RV and travel-trailer guides, both diagnostics and the published method.