Every inverter gets a score from 0 to 100% built from six factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Inverters are ranked within their size (up to 1,000 W, 1,100 to 2,000 W, over 2,000 W), and inverter-chargers on their own page, each on its own price and idle-draw scale.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per continuous watt | 30% |
| Idle draw | battery drain with nothing plugged in | 15% |
| Safety listing | UL 458 or UL 1741 listing | 15% |
| Warranty | warranty length | 15% |
| Features | remote, app, transfer switch or lithium charging, hardwire terminal, display | 15% |
| Efficiency | peak efficiency | 10% |
Where the numbers come from
Power ratings, idle draw, efficiency, listings, features and warranty come from the maker’s datasheet, manual, product page or warranty page. Some budget brands publish nothing beyond their store listing; where that’s the only source, the product page says so. Surge ratings in particular are often inflated by budget brands, which is one reason surge isn’t scored.
The factors
Value is the price divided by the continuous power rating: dollars per watt. Small inverters cost more per watt, and inverter-chargers include a charger and transfer switch, so each has its own scale.
| Size | Scores 0 | Full marks |
|---|---|---|
| Up to 1,000 W | $0.60 per watt | $0.12 per watt |
| 1,100 to 2,000 W | $0.45 per watt | $0.09 per watt |
| Over 2,000 W | $0.40 per watt | $0.08 per watt |
| Inverter-chargers | $1.00 per watt | $0.25 per watt |
Idle draw is the current the inverter takes from a 12 V battery when it’s switched on with nothing plugged in (power saving off). It runs all day whether or not you use the inverter, so it decides whether you can leave it on. Bigger inverters naturally idle higher, so the scale grows with size.
| Size | Scores 0 | Full marks |
|---|---|---|
| Up to 1,000 W | 12 W (1 A) | 3 W (0.25 A) |
| 1,100 to 2,000 W | 24 W (2 A) | 6 W (0.5 A) |
| Over 2,000 W | 36 W (3 A) | 9 W (0.75 A) |
| Inverter-chargers | 40 W (3.3 A) | 10 W (0.8 A) |
Safety listing is full marks for an inverter that the maker says is listed or certified to UL 458 (the US standard for inverters in vehicles and boats) or UL 1741 by a test lab such as UL, Intertek (ETL), CSA or TÜV, and zero otherwise. “Meets UL 458” or a logo on a store photo doesn’t count, and FCC and CE marks aren’t safety listings. A listing the maker doesn’t mention counts as none, since makers that have one advertise it.
Warranty: 1 year scores zero and 5 years full marks.
Features adds up the things that make an inverter easier to live with:
| Feature | Share of the factor |
|---|---|
| A wired remote switch or panel in the box (half credit if sold separately) | 25% |
| A Bluetooth or Wi-Fi app built in (half credit for an add-on dongle) | 25% |
| Inverters: a built-in transfer switch; inverter-chargers: a lithium (LiFePO4) charge profile | 25% |
| A hardwire terminal for wiring into an RV or cabin’s outlets | 15% |
| A readout on the unit | 10% |
A feature the maker doesn’t state either way gets half credit.
Efficiency is the maker’s peak efficiency: 85% scores zero and 94% full marks. Real efficiency at light loads is lower and is rarely published, and peak figures aren’t measured the same way by every maker, so this factor carries the least weight.
What isn’t scored
Surge power, the number of outlets, USB ports, GFCI protection, charger current, parallel operation, cooling, size and weight are listed but not scored. Independent tests are listed where they exist, but there are too few to score.
Missing data
If a figure other than the safety listing isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each size. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.