On this page 8 sections
Buying a power station is a sizing decision as much as a brand decision. This page explains how we evaluate products, where our data comes from, and how we calculate the runtimes you see across the site.
Where our data comes from
The sources behind every number
- Product specifications: capacity, output, charging, cycle life and warranty come from each product's official specifications, product page or manual, and are re-checked whenever we update an article.
- Runtime figures: our own calculations from those specs, using one method across the whole site (below).
- Hands-on testing: when we test a unit ourselves, we keep a test log and say so in the article. We never claim a test we didn't run.
How we calculate runtime
One formula, used on every page
All runtime estimates on this site use the same formula:
Runtime (hours) ≈ capacity (Wh) × 0.85 ÷ average load (W)
- Why 85%? Power is lost converting the battery's DC power to the AC power your devices use, and in the battery system itself. Real efficiency varies by model and load; 85% is a reasonable planning figure for AC loads. DC loads (USB, 12 V) are usually more efficient.
- Average load, not peak. Fridges, freezers and pumps cycle on and off. We use average draw over time, which is much lower than the running wattage on the label.
- Surge matters separately. Motors and compressors need a short burst of extra power to start. We check that a station's surge rating can handle it before recommending it for that appliance.
- Real life varies. Cold temperatures, battery age, inverter idle draw and how often an appliance cycles all change real runtime. Treat our numbers as planning estimates, not guarantees.
What we evaluate
The criteria behind every recommendation
| Criterion | What we look at |
|---|---|
| Capacity & usable energy | Rated watt-hours; usable energy where tested |
| Output | Continuous AC watts, surge watts, outlet types (including RV and 240 V where relevant) |
| Charging | AC charge time, solar input watts and voltage range, car charging |
| Battery | Chemistry, rated cycle life, warranty length |
| Backup features | UPS/EPS switchover time, pass-through charging |
| Portability | Weight, size, handles and wheels |
| Expandability | Extra batteries, maximum system capacity |
| Ecosystem & support | App, firmware updates, warranty terms, recall history |
| Value | What you get per watt-hour and per year of warranty, rather than a fixed price |
The weight of each criterion depends on the guide. For a CPAP guide, quiet operation, DC output and weight matter most; for home backup, capacity, surge and expandability matter most.
How we rate products
A 0–10 score from published specs
Every review shows an OffGrid Current rating out of 10. It's calculated the same way for every station, from the published specifications in our product data, using the fixed weights below. It isn't based on hands-on testing, and no brand can pay for a better score. Where a spec isn't published, that criterion gets a low "unknown" score rather than a guess.
| Criterion | Weight | How it's scored (0–10) |
|---|---|---|
| Wall charging speed | 20% | AC input watts per Wh of battery, scaled by size class (see below) |
| AC output | 20% | Continuous watts, scaled by size class (see below) |
| Solar input | 10% | Solar watts per Wh of battery: 0.2 → 0, 0.8 or more → 10 |
| Backup switchover | 15% | 10 ms or less → 10, 15 ms → 8, 20 ms → 6, not stated → 3 |
| Portability | 10% | Wh per lb, scaled by size class (see below) |
| Expandability | 10% | None → 0, add-on battery via power-bank mode → 4, 2× capacity → 7, 5× or more → 10 |
| Battery life & warranty | 15% | 5-year warranty → 6 (3 years → 4, 2 years → 2); plus 4,000+ cycles → 4, 3,000+ → 3, fewer → 2, not stated → 1 |
Charging, output and portability are scored against the station's size class:
| Size class | AC output (W) | Charging (W per Wh) | Wh per lb |
|---|---|---|---|
| Compact (under 1 kWh) | 150 → 600 | 0.3 → 1.5 | 20 → 45 |
| Mid-size (1 to 1.5 kWh) | 800 → 2,400 | 0.3 → 1.5 | 20 → 45 |
| Large (2 to 3 kWh) | 1,500 → 3,000 | 0.3 → 1.2 | 20 → 50 |
| Whole-home (3.5 kWh and up) | 3,000 → 6,000 | 0.2 → 0.8 | 15 → 35 |
Compact stations (under 1 kWh) are rarely bought for UPS backup or expansion, so they aren't scored on those two criteria; portability and battery life & warranty count 25% each instead.
Each range runs from a score of 0 to 10. Method version 1.4 (2026-11-13): size classes aligned with the sitewide size bands.
Each review's verdict card shows the overall rating and a breakdown by criterion. When a manufacturer corrects a spec, the rating updates with it. If we change the method, we update this page and every rating at the same time.
Hands-on testing
What we record when a unit is on our bench
When we test a unit hands-on, we record:
- Usable capacity: energy delivered at a fixed, steady load from full charge until shutdown, compared with the rated figure.
- AC charge time: from empty to full on wall power, in the fastest standard mode.
- Real appliance runs: for example, running a refrigerator or CPAP and logging energy used over time.
- Noise: sound level at a set distance under load.
- Solar input: observed charging watts under recorded conditions.
Articles say when a product has been tested hands-on. Products we haven't tested are evaluated from their specifications and our runtime calculations.
What we will never do
Our non-negotiables
- Claim we tested, owned or used a product when we didn't.
- Invent measurements, quotes, reviews or expert credentials.
- Let a brand pay for a placement or a better rating.
- Show prices that aren't current, or ratings from anywhere other than the method above.
Free or loaned products
How we handle products from manufacturers
If a manufacturer gives or lends us a product, we say so in the article. It doesn't buy a positive review, and products are returned or disclosed according to the arrangement.
Updates
Keeping guides current as products change
Power stations change quickly, with new generations, firmware and prices. We re-check our buying guides regularly and whenever a product changes. Material corrections are noted under our corrections policy.