About WattLark

WattLark helps you keep the essentials running when the power goes out: what size of backup you need, what it will and won't run, and which units are worth it.

How we evaluate

We don't run a test lab, and we won't pretend to. Every recommendation is built from three things you can check yourself:

• Manufacturer specs, labeled as such wherever they appear.
• Runtime math we show. Every estimate lists its assumptions right next to the number.
• Trade-offs, stated plainly. Every pick names its downside.

How we label numbers

Manufacturer spec

Published by the brand. We report it, we don't verify it.

Our estimate

Calculated by us from specs and published usage data, with the assumptions shown.

Tested

Reserved for numbers we measure ourselves. We'll only use it once we do.

How we calculate runtime

Runtime in hours = rated capacity (Wh) × 0.85 ÷ daily use (Wh) × 24.

The 0.85 assumes about 85% of a battery's rated capacity is usable after inverter and conversion losses. Appliances that cycle on and off, like fridges and freezers, use their daily kWh, which already includes cycling. Everything else uses watts × hours on per day.

When we don't know your exact appliance, we show a range from an efficient model to a large one. A typical fridge uses 1.1 to 1.9 kWh a day (ENERGY STAR), so a 2,048 Wh unit gives about 22 to 38 hours. We round to whole hours, and show days above 72 hours.

We only say a unit "covers" an outage when the low end of our estimate reaches the full outage length. Medical devices are sized first, with the settings we assumed shown next to the number.

How we make money

When you buy through our links, the retailer may pay us a commission. It doesn't change what you pay, and it never changes which unit we recommend. Nothing on WattLark is sponsored. Full affiliate disclosure

Corrections and contact

Spot a number that's wrong or out of date? Tell us and we'll fix it and note the change at the end of the page. Email hello@wattlark.com.