Watt-hours, watts, battery chemistry and what a campsite load really needs, worked through with simple arithmetic you can repeat for your own gear.
The biggest number on a power station's box is rarely the one that tells you how long it will run your gear. Two ratings do that job, and they answer different questions. One describes how much energy is stored; the other describes how much can be delivered at once. Once you can tell them apart, the rest of the product page becomes much easier to read.
Capacity is quoted in watt-hours (Wh). A 500 Wh unit can, in theory, supply 500 watts for one hour, or 50 watts for ten. Output is quoted in watts (W), usually as a continuous figure for the AC inverter plus a higher short-term surge figure. Think of Wh as the size of a water tank and W as the width of the pipe leaving it. A big tank with a narrow pipe will run small things for a long time; a small tank with a wide pipe can start a heavy appliance and empty itself in minutes.
Phone-style milliamp-hour (mAh) figures are less useful here because they depend on cell voltage. Battery University lists typical lithium-ion cells at 3.6 to 3.7 V nominal and lithium iron phosphate (LiFePO4 or LFP) at 3.2 to 3.3 V, so the same mAh means different energy in each. Multiplying volts by amp-hours gives watt-hours, and that is the figure to compare.
Converting battery power to a household-style AC outlet loses some energy as heat. Makers' figures vary, so the examples here assume 85% of the rated capacity is usable. That percentage is an assumption for illustration, not a measured or published value; a 500 Wh unit becomes 425 Wh.
Look on the label or power supply. Chargers often show volts and amps instead, and volts multiplied by amps gives watts.
Usable Wh divided by device watts gives hours.
Add up everything that runs at once and compare it with the unit's continuous output rating. Anything with a motor or heating element may need much more at start-up than its running figure.
| Load | Example draw | Approximate runtime | What it shows |
|---|---|---|---|
| LED lantern | 5 W | 85 hours | Light loads stretch a small unit across days |
| Phone charging | 15 W | about 28 hours of charging | Capacity is rarely the limit for phones |
| Laptop | 60 W | about 7 hours | A day's work, not a weekend's |
| Compact fridge | 40 W average (higher at compressor start) | about 10 hours | Cycling loads make real runtime hard to guess |
| Electric kettle | 1,500 W | about 17 minutes | A heating appliance can empty a small unit quickly, and a 1,000 W inverter could not start it at all |
The pattern is the useful part. Anything that makes heat, such as kettles, hair dryers, space heaters and toasters, draws far more than anything that makes light or charges a battery. Camping with a power station is mostly a matter of keeping heat-making jobs on a stove.
Battery University's comparison table gives LiFePO4 a cycle life of 2,000 and higher, against 1,000 to 2,000 for NMC (nickel manganese cobalt) lithium-ion, and a thermal-runaway temperature of 270 °C against a typical 210 °C. The trade-off is energy density: 90 to 120 Wh/kg for LiFePO4 against 150 to 220 Wh/kg for NMC. As rough cell-only arithmetic, 1,000 Wh at 100 Wh/kg is 10 kg of cells, while at 200 Wh/kg it is 5 kg. The finished unit weighs more once the case, inverter and electronics are added, but the direction holds: longer life and a higher failure-temperature threshold usually come with extra mass.
Cycle ratings are laboratory estimates and Battery University notes that real-world life is often shorter. A power station used at a few weekends a year will rarely come near its cycle count; the calendar will matter first. For those users weight and portability may count for more.
For lithium-ion, Battery University gives a charging range of 0 °C to 45 °C and a discharging range of -20 °C to 60 °C. Charging below freezing can plate metallic lithium on the anode, which causes permanent loss of performance and safety even if the pack seems to charge normally. A power station left in a frosty car boot or tent overnight is therefore best brought to above freezing before charging; the manufacturer's manual should state the exact limits for the model.
Canada's air-security authority CATSA publishes guidance for lithium-ion batteries rated 101 to 160 Wh: in a device they can go in carry-on or, with air carrier approval, checked baggage, and no more than two protected spares are allowed per person in carry-on with approval. Transport Canada says spare lithium batteries, including power banks, must be in carry-on baggage only, and the UK Civil Aviation Authority says power banks belong in the cabin and should never be charged in flight.
None of those passenger limits reaches beyond 160 Wh, and the example 500 Wh unit is more than three times that (500 ÷ 160 ≈ 3.1, illustrative arithmetic). Most power stations sit well above the ceiling. Treat them as something to buy at your destination or have shipped by a carrier that handles dangerous goods, and check with your airline before travelling.
Only if the manual says so. Many are not rated for water, and where a rating exists, check what it covers. When in doubt, keep it under cover and off wet ground.
Conversion losses, cold, and peaks above a device's label figure all eat into the total. Treat any runtime sum as an upper estimate.
How we research. Based on manufacturer documentation and the sources listed below. Know Your Gadget did not test products for this article. See our editorial policy.
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