How we rate
Every number on this site traces back to a spec database and a documented model. This page is the documentation.
The WattScore
WattScore is a 0–100 editorial score computed across five weighted axes, applied identically to all 14 stations on the bench:
- Usable capacity25%
- Rated Wh adjusted for chemistry and realistic inverter losses — a 1,024Wh LFP unit and a 1,024Wh NMC unit are not the same product three years in.
- Inverter strength25%
- Continuous output, surge headroom, and how much of the household load map (fridge, sump pump, kettle) the unit actually clears.
- Charge speed & inputs20%
- AC fast-charge time to 80%, max solar input, and whether you can charge while discharging — the spec that matters most in a multi-day outage.
- Chemistry & longevity15%
- LFP (3,000+ cycles) scores above NMC (~500–800 cycles). Warranty length and BMS behavior feed in here.
- Value15%
- Wh and inverter watts per dollar inside its price band — a station only competes against what else your budget buys.
Runtime modeling
Runtime estimates across the site (calculator, Can It Run pages, head-to-heads) use one formula: rated capacity × 0.85 inverter efficiency, divided by duty-cycle-weighted running watts. Surge verdicts require the station's surge rating to cover the load's startup spike stacked on other running loads. Appliance figures are typical US residential values across our 20-load database — check your unit's nameplate, because models vary.
Where the specs come from
Manufacturer datasheets and manuals, recorded at the time each station is added to the database and re-checked when revisions ship. Price bands reflect typical street pricing, not live offers.
Commissions and the firewall
WattRatings earns affiliate commissions — including from Amazon — when you buy through our links. Scores and verdicts are computed from the spec database before any link is attached, and no manufacturer sees, sponsors, or edits a rating. If a product is bad, the score says so and the link stays anyway. See the full affiliate disclosure.
Corrections
Spot a spec we got wrong? Tell us — database corrections ship site-wide, since every page reads from the same source.