How we choose products

1. Official documents only

We read each product's spec page, user manual, installation guide and warranty terms on the maker's own site, and note the date we checked them. If a figure can't be confirmed from an official source, we leave it out rather than guess. When a maker's own pages disagree, we use the spec table or the manual, and the guide says so. When a fact appears only outside the spec table, such as in a maker's FAQ or blog, the guide says where it comes from.

2. Safety listings, quoted exactly

We quote each maker's listing claim in its own words, and where the wording is vague ("UL" with no standard named, or "certificated" instead of listed), the guide says exactly that. The standards we look for:

• UL 2743: portable power packs, meant for use when grid power isn't available.
• UL 9540: energy storage systems. UL Solutions says the model installation codes require it for a stationary battery system in a home.
• UL 2252: adapters for EV charging couplers, such as J1772-to-NACS adapters.
• EV chargers: a listing from a nationally recognized testing laboratory, such as UL, Intertek (ETL) or CSA.

3. The arithmetic, shown and labelled

Every calculation is shown and labelled as an estimate. We never promise a runtime or a charging time.

• Runtime: capacity in watt-hours, times the usable share after inverter losses, divided by the load plus the station's own draw. Where a maker publishes these factors, we use them; otherwise we state our assumption.
• Solar fit: the open-circuit voltage of panels wired in series has to stay inside the station's solar input window, and the watts within its maximum.
• Charging power: kW = amps × volts ÷ 1,000. EV charging is a continuous load, so the circuit is sized at 125% of the charging current, as the chargers' installation guides state.
• Range per hour of charging: kW ÷ the car's EPA consumption in kWh per 100 miles × 100.

4. Matching products to real jobs

We tag each product with the jobs it suits, such as camping, home backup, solar charging, Tesla and NACS cars, or J1772 cars, and check it against the buyer's real limits: an appliance's running and start-up watts, the home's circuit, and the car's charge port and onboard charger.

5. Value and track record

We favour current models from established makers with full documentation, clear warranty terms and support pages, and we mention owner-reported patterns only when they're widely documented. We never use star ratings, review counts or sales ranks.

6. Recalls

Before a product goes into a guide, and again at each refresh, we search the US Consumer Product Safety Commission's recall database for the brand and the model.

7. Dates you can trust

A guide's Updated date changes only when its content changes, and each guide says when its specs were last checked against the makers' pages.

What we don't claim

thisWATT is a research publication. We haven't lab-tested the products we cover, and we never present spec-sheet research as test results. If measurements from our sister site thisMETER are ever used in a guide, the guide will say so and explain how they were taken. We never give wiring or installation instructions: home backup connections and hardwired EV chargers are a licensed electrician's job. We earn commissions on some purchases through our links, and they never decide a pick; see the affiliate disclosure.