How Long Does a Power Station Last on a Charge

Every power station box has a runtime chart on the back. Find your device’s wattage, read across, and there’s your answer — clean, confident, wrong. Those numbers are calculated by dividing rated watt-hours by device wattage and stopping there. No inverter losses, no battery cutoff margin, no compressor surge. The result is a best-case ceiling that real use can’t reach, and for certain loads, won’t even come close to.

The actual picture is messier but not hard to work with once you know what the label leaves out. This guide walks through the real runtime math, the loads that blow up clean estimates, and the battery lifespan figures manufacturers love to quote — so you can size your expectations before you size your gear.

The Efficiency Tax Every Runtime Estimate Hides

The math on a manufacturer’s chart is simple: rated watt-hours divided by device watts. A 1,000Wh unit running a 100W load — ten hours. Neat. But that assumes every watt-hour stored comes out the other end as usable AC power, and that’s not how inverters or batteries work.

In reality, the inverter converting DC battery power to AC loses a cut of everything passing through it. The battery’s internal management system reserves some capacity at the bottom to protect the cells. Add those together and you’re working with roughly 80–90% of the rated capacity as actual, usable AC output. That same 1,000Wh unit running a 100W load doesn’t give you ten hours — it gives you closer to eight or nine.

That gap is consistent across the category. The manufacturer’s own runtime tables — which are the dominant source of specific numbers in this space — are built on naive division with no efficiency derating. They reflect the ceiling the physics allows, not what a real load sees. Think of the rated Wh as the tank size and the usable Wh as the fuel that actually reaches the engine: always a bit less, sometimes meaningfully so.

A few things push you further toward the low end of that 80–90% window:

• AC output is lossier than DC or USB. The inverter only runs when you’re using the AC outlets. DC and USB outputs bypass most of that conversion, so phone charging or a 12V device runs more efficiently than anything plugged into a wall-style socket.
• Cold temperatures shrink real capacity. Battery chemistry slows in the cold, and you’ll notice it as shorter runtimes on chilly nights even on a full charge.
• Cheaper and smaller units tend to have less efficient inverters. The efficiency penalty is real at any price point, but it’s more pronounced at the entry level.

Wattage Is the Whole Game — Which Is Why “3–13 Hours” Means Nothing

Runtime is entirely a function of two variables: battery capacity in watt-hours and load in watts. There is no “typical” runtime for a power station any more than there’s a typical fuel range for a car without knowing the tank size and the engine.

The “3–13 hours” figure that circulates online is a good example of a number that sounds informative and isn’t. No stated capacity, no stated load — it’s a range so wide it fits almost any scenario and tells you nothing useful about yours. Discard it.

The relationship that actually matters is direct and proportional: cut the load in half and the runtime doubles. Double the load and the runtime halves. That’s the spine of every honest runtime estimate. Here’s what that looks like across real wattage tiers, using manufacturer-supplied figures as a best-case reference — remember to apply the 80–90% usable efficiency before treating these as real expectations:

Shave 10–20% off those marketed hours to get into the real-world zone. The low-draw devices — lights, CPAP, phones — are where a power station genuinely shines. The high-draw resistive loads (anything that heats or does heavy mechanical work) are where battery capacity evaporates fast.

There’s also a limit that has nothing to do with battery size: the inverter’s continuous wattage rating. A 1,500W load won’t run on a unit whose inverter is rated for 1,000W continuous — full stop, regardless of how many watt-hours are in the pack. Runtime doesn’t matter if the thing won’t start. Check the inverter’s continuous output spec against your intended load before assuming capacity alone is the deciding factor.

Fridges Are the Exception That Breaks Clean Math

If you’re buying a power station to run a refrigerator — for a camping trip, a power outage, or an off-grid setup — the steady-state wattage figure is almost beside the point.

Fridge compressors surge on startup. That initial draw can reach several times the running wattage before settling. If that surge exceeds the inverter’s rated surge capacity, the unit either trips protection or shuts down entirely. You’ll see the unit restart, struggle, or fail to hold the load — none of which shows up in a runtime chart calculated on steady-state watts.

The numbers already don’t agree at the steady-state level: one manufacturer uses 100W in its fridge runtime math (producing an attractive ~10-hour figure), while another source quotes 150–200W as a more realistic steady draw. That discrepancy matters, but the surge is the bigger issue neither source addresses. The takeaway is practical:

• Check the inverter’s surge watt rating, not just its continuous rating.
• Look up your fridge’s actual startup wattage (often on the data plate or in its manual) — it will be higher than the running wattage, sometimes dramatically so.
• The manufacturer’s “X hours for a fridge” figure is probably both using an optimistic steady-state draw and ignoring whether the inverter can even handle the startup event.

This is where real-world fridge runtimes diverge most sharply from what’s printed on the box.

Battery Lifespan: What Cycle Numbers Do and Don’t Tell You

Power station marketing leans hard on cycle life, and the chemistry comparison is the one genuinely useful signal in those claims: lithium iron phosphate (LiFePO4) cells are rated for significantly more cycles than older lithium-ion (NMC) chemistry — roughly 2,000–3,500+ cycles versus 500–800 cycles. The direction of that comparison reflects real electrochemistry and is worth knowing when you’re choosing between units.

Everything else in this space deserves more skepticism. All specific cycle figures here come from a single manufacturer’s marketing materials, and there’s a structural reason to hedge: no one cycles a unit thousands of times in a review window to verify it. These are datasheet projections, not independently measured outcomes.

A few things the cycle number doesn’t tell you:

• What “a cycle” counts as. These ratings are typically measured to 80% remaining capacity — meaning the battery is considered “dead” when it holds 80% of its original charge. That threshold is often omitted entirely from the headline number.
• What degrades the rating in real life. Frequent full charges to 100%, deep discharges, heat from heavy use or storage in a hot car — all of these shorten real-world cycle life below the spec. The datasheet number assumes controlled conditions.
• What “10+ years” actually requires. That figure assumes moderate use — roughly one cycle every day or two. Daily deep cycling shortens the timeline substantially.

The honest read: LiFePO4 lasts considerably longer than NMC, and the cycle counts give you a rough ordering, not a guarantee. Treat the specific numbers as directional, not contractual.

A Simple Framework That Actually Works

You don’t need a complex calculator. You need three steps:

1. Multiply rated Wh by 0.85 (or use 0.80 as a conservative floor) to get your real usable capacity. That’s your honest starting point.
2. Divide by your device’s actual running wattage — the number it draws during steady operation, not the peak or the startup surge. For motors and compressors, look up or measure the running draw separately.
3. Check the inverter’s continuous and surge ratings against your highest-draw device. If your load exceeds the continuous rating, runtime is irrelevant — it won’t run.

The manufacturer’s chart on the box isn’t useless — it tells you the best-case ceiling and lets you compare units on the same terms. It just isn’t what you’ll live with. Knock 10–20% off any printed runtime and you’re in the real world. For fridges and compressor loads, that discount is bigger, and the surge spec matters more than the watt-hours do.