Quick answer: Power station capacity is quoted in watt-hours, which measure stored energy. Amp-hours measure nothing unless the voltage sits beside them: one maker rates a single 1,000 Wh battery at both 19.5 Ah and 312 Ah, and both are correct. Roughly 15 to 40 per cent never reaches your appliance.
The number on the box is the first thing you compare and the least well explained thing on the product page. Two things make it confusing: the industry quotes two different units for the same battery, and the rated figure describes what the cells hold rather than what the sockets deliver. For the purchase decision itself, our power station sizing guide turns all of this into a capacity to buy.
Power station capacity: only the watt-hour survives comparison
A watt-hour is energy: one watt drawn for one hour. An amp-hour is charge, and charge becomes energy only once you know the voltage it sits at. The clearest published statement of the conversion comes from aviation law. The FAA puts it plainly: “To determine Wh, multiply the volts (V) by the amp hours (Ah). Example: A 12-volt battery rated to 8 Ah is rated at 96 Wh”.
Watt-hours are used because amp-hours cannot be compared between batteries. Spare lithium-ion batteries are capped at 100 Wh, with 101 to 160 Wh allowed only by airline approval and anything above 160 Wh forbidden. You can see that limit in the catalogues. Jackery sells a 99 Wh unit it calls a portable power station and markets as “carry-on power for flight” — one watt-hour under the line. The next model up its range is 256 Wh, already 60 per cent above the absolute 160 Wh ceiling. There is nothing between the two in that catalogue, and no reason for there to be.
What one manufacturer publishes for its own line-up
Goal Zero prints the voltage, the amp-hours and the watt-hours for every model, which makes it the only line-up whose arithmetic you can check. Every figure below is theirs.
| Model | Chemistry | Published capacity | Pack V × Ah | Same pack, per cell |
|---|---|---|---|---|
| Yeti 150 | AGM lead acid | 168 Wh | 12 V × 14 Ah | not published |
| Yeti 1000 Lithium | Li-ion NMC | 1,045 Wh | 10.8 V × 96.8 Ah | 3.6 V × 290.44 Ah |
| Yeti 1000 | LiFePO4 | 998.4 Wh | 51.2 V × 19.5 Ah | 3.2 V × 312 Ah |
| Yeti 3000X | Li-ion NMC | 3,032 Wh | 10.8 V × 280.8 Ah | 3.6 V × 842.4 Ah |
| Yeti 6000X | Li-ion NMC | 6,071 Wh | 10.9 V × 556 Ah | 3.6 V × 1,668 Ah |
Read the two Yeti 1000 rows together. Same company, same size of battery — 998.4 Wh against 1,045 Wh — and one is rated 19.5 Ah, the other 96.8 Ah. Neither is wrong: the LiFePO4 pack wires its cells to 51.2 V and the older NMC pack to 10.8 V.
Then look at the last column, which is where the trap closes. Goal Zero also publishes a single cell equivalent capacity — the same stored energy counted at the voltage of one cell instead of the whole pack. By that measure the LiFePO4 unit is 312 Ah and the NMC one is 290.44 Ah. So one manufacturer, describing about one kilowatt-hour, honestly publishes 19.5, 96.8, 290 and 312 amp-hours. A factor of sixteen, and not one of those numbers is a lie.
An amp-hour figure quoted without its voltage is not a specification. If a listing gives you amp-hours alone, the number it is hiding is the one you needed.
Where the missing capacity goes
The rated power station capacity describes energy stored in cells. Your appliance sits on the far side of an inverter, and four things stand between the two.
- Conversion. Turning DC into 120 V AC costs a percentage — the loss everyone has heard of, and the smallest of the four on light loads.
- Idle draw. The inverter burns a few watts simply being switched on, whether your load is 10 W or 1,000 W. On small loads that dominates — which is why a 12 V appliance on the DC output gets far more out of the same battery.
- The reserve the battery keeps. A management system stops the discharge before the cells are empty, because taking a lithium cell to zero shortens its life. That reserve sits inside the rated figure. Fixed home batteries normally publish a separate usable figure; portable ones almost never do.
- Temperature. Goal Zero publishes a discharge range of −4 °F to 104 °F for its LiFePO4 model but a charge range of only 32 °F to 104 °F. Below freezing that unit will run your loads and refuse to take a charge.
Add them up and somewhere between 60 and 85 per cent of the rated watt-hours reaches an AC load, worst at the small loads people buy these things for. Rated capacity divided by appliance watts is not a conservative estimate; it is an optimistic one.
The arithmetic the industry itself publishes
Goal Zero’s support pages teach the division with no losses at all: “a 500Wh battery should run a 100W light for 5 hours (500/100=5)”. A second manufacturer’s published runtimes show how far that lands off.
EcoFlow’s runtime table for the DELTA 2 gives 89 charges of an 11 Wh phone, which is 979 Wh delivered. Divide that by a 10 W light and the simple method predicts 98 hours. The same table publishes 58 hours for a 10 W light. The simple method overstates by 69 per cent — not because either figure is wrong, but because one of them goes through the inverter and the other does not.
How we calculated this
Every capacity, voltage and amp-hour figure here is copied from a manufacturer’s published specification and checked by multiplying it out; four of the five Goal Zero models reproduce their stated watt-hours to within 0.1 per cent. The FAA limits and the conversion example come from FAA pages read on 4 September 2026. The 60 to 85 per cent band is ours, derived from EcoFlow’s published runtimes for constant AC loads, and quoted wide because no maker publishes a delivered-energy figure and we have not measured one. No product was tested by us and none is recommended; both manufacturers appear only as documents. Our method is described at how we test.
Before you store one in an unheated space
Do not charge a lithium battery below its published charge temperature range. Charging a cell below freezing damages it permanently, and that is a safety matter rather than a performance one. Most units refuse on their own; do not defeat that.
Frequently asked questions
How do I convert amp-hours to watt-hours?
Multiply the amp-hours by the nominal voltage — the FAA’s own example is a 12-volt battery rated at 8 Ah, which is 96 Wh. For milliamp-hours, divide by 1,000 first. You need the pack voltage rather than a cell voltage, and that is the figure listings tend to omit.
How much of the rated capacity do I actually get?
Plan on about 80 per cent through an AC socket — the figure our sizing guide builds its runtimes on — and less below roughly 20 W where the inverter’s idle draw is a large share of the total. What that buys at 1,000 Wh is a table of its own. Through a USB or 12 V output the inverter is bypassed and you keep more. That is a planning assumption, not a specification: no manufacturer publishes a delivered-energy figure.
Can I take a power station on a plane?
Almost certainly not, unless you bought one specifically for it. Lithium-ion batteries above 160 Wh are forbidden in both carry-on and checked baggage, which rules out every unit big enough to run a fridge. The exception is a small class built to the rule — 99 Wh models sold as travel power banks, under the 100 Wh carry-on threshold. The test is the watt-hour rating marked on the unit, not the model name.
Does a bigger capacity mean it can run bigger appliances?
No — that is the inverter’s continuous and surge ratings, separate specifications quoted in watts. Capacity buys duration, not capability. A large battery behind a small inverter will still refuse to start a refrigerator’s compressor, and the gap between starting and running watts is where most sizing goes wrong.
The short version
Compare watt-hours and nothing else, and treat any amp-hour figure without a voltage beside it as missing information. Knock the rated watt-hours down by about a fifth before dividing by your appliance’s running watts. Then check the charge temperature range, usually stricter than the discharge one, and what the cycle rating is measured to: 4,000 cycles to 80 per cent of original capacity is a reminder that rated watt-hours are a new-battery number.
This article is general information, not an installation guide and not a substitute for a licensed electrician. Electrical work on a service panel, a transfer switch or a utility connection is regulated in most jurisdictions and normally requires a permit and an inspection. Fuel-burning equipment produces carbon monoxide and must never be run indoors, in a garage or near an opening into the home.
