How we size and score backup power
Size the Load does not operate an in-house test lab in 2026. We do not claim that we personally discharged every unit on this site.
Every recommendation has to survive three questions: Can the inverter start the load? Can the battery run it for the hours you need? Is the chemistry and warranty worth the price per usable watt-hour?
Where numbers come from
- Manufacturer specification sheets and user manuals for rated watt-hours, continuous watts, surge watts, solar input, chemistry, cycle life, and weight.
- Independent measurements when a trusted lab has published them.
- Typical appliance figures from EnergyGuide labels and widely reported duty-cycle ranges. We state the assumption next to every runtime.
- Owner reliability themes from warranty terms and repeated public failure reports. These are qualitative, and we label them that way.
Default math
Unless a page names a different test, we convert sticker capacity with an 85% usable factor. That is a conservative planning number, not a promise.
Runtime hours ≈ (rated Wh × 0.85) ÷ average watts.
Average watts ≈ running watts × duty cycle. A refrigerator compressor is often on 30–40% of the day. A CPAP is closer to continuous.
A station is a candidate only if continuous watts exceed running watts and surge watts exceed compressor or motor start watts.
Scoring rubric
- Usable capacity & efficiency — 25%
- Real output — 20%
- Charge speed — 15%
- Use-case fit — 15%
- Chemistry, cycles, service — 15%
- Price per usable Wh — 10%
There is no extra score for a higher affiliate commission.
What we will not do
- Feature an unbranded marketplace station as Best Overall.
- Publish a runtime without stating the load and duty cycle.
- Pretend a 300 W travel station will start a French-door refrigerator.
- Give medical or electrical-code advice.