How to Calculate Portable Power Station Runtime

A portable power station’s runtime is roughly its usable energy divided by what your devices draw. Take the capacity printed on the unit in watt-hours (Wh), take off a share for energy the battery holds back and energy lost in conversion, then divide by the total watts of everything plugged in.

Runtime (hours) = rated capacity (Wh) × usable fraction × efficiency ÷ load (W)

If you don’t know the usable fraction and efficiency for your unit, multiplying the rated Wh by about 0.85 is the shortcut several manufacturers publish for AC loads. Treat the answer as a planning number. Startup surges, compressors that cycle on and off, heat, idle draw and an ageing battery all change the real figure. This guide explains each one, with worked examples you can repeat in our power station runtime calculator.

The terms you need

• Watt (W): how fast a device uses power at a given moment. An electric fan might draw 60 W.
• Watt-hour (Wh): an amount of energy. One watt for one hour is 1 Wh. In theory a 1,000 Wh battery could supply 100 W for 10 hours.
• Inverter: the part inside the power station that converts the battery’s direct current (DC) into alternating current (AC) for the outlets you plug household appliances into.
• Depth of discharge (DoD), or usable fraction: the share of the battery’s capacity the unit actually lets you use.
• Continuous (rated) output: the most AC power the inverter can supply steadily, in watts.
• Surge (peak) output: a higher wattage the inverter can supply for a moment, for example when a motor starts.

If a spec sheet lists capacity only in amp-hours (Ah), convert it with the battery voltage printed next to it: Wh = Ah × volts.

What manufacturers say about the runtime formula

Power station makers publish simple runtime formulas, and they are close to each other:

BLUETTI’s version is the most detailed because it separates the two losses and adds the unit’s own power use. It says most LiFePO4 batteries allow 80–95% of their capacity to be used, and that inverters in good units typically reach 85–95% efficiency. Multiply its example values (0.95 × 0.90) and you get about 0.86, very close to the 0.85 the others use.

So 0.85 is a sensible default for AC loads when you have nothing better. If your manual lists a DoD or efficiency figure for your unit, use those instead. Jackery’s own FAQ adds that actual power consumption varies with use, which is a fair warning for every brand.

Rated capacity vs usable capacity

The Wh figure on the box is the battery’s rated capacity. You won’t get all of it at the outlet, for two separate reasons:

1. The battery holds some back. The battery management system stops the discharge before the cells are completely empty. That reserve protects the battery, and the usable fraction (DoD) describes it.
2. Conversion wastes some energy. Turning the battery’s DC into AC produces heat. EcoFlow puts this loss at typically 10–20%, and says a 1,000 Wh battery may supply only about 800–900 Wh of usable AC power.

When you compare units, compare the rated Wh, and also look for any stated usable capacity, DoD or efficiency figure in the manual.

AC outlets vs DC outputs

The inverter loss applies to the AC outlets. USB ports and the 12 V car-style socket skip the DC-to-AC step. They still convert voltage internally, so they are not loss-free, but they avoid the inverter. BLUETTI says using DC ports where possible can extend runtime by up to 15–20%.

Two inverter effects matter for small household loads:

• Idle draw. BLUETTI notes that keeping the AC inverter switched on uses power even with nothing plugged in, and that idle draw matters most with light loads and long backups. If you only need USB or 12 V that night, switch the AC output off.
• Poor efficiency at very light loads. According to BLUETTI, inverters are least efficient at very low loads, typically below 10–20% of their rated output. A 70 W fan-and-router load on a unit with a large inverter may convert less efficiently than the headline figure suggests.

Phones, power banks, LED lamps, many routers and some fans can run from USB or 12 V. Only use cables and adapters that match the device’s voltage and plug. If you’re unsure, use the AC outlet with the device’s own adapter.

Continuous output, surge output and startup loads

Runtime is about energy. Whether the unit can run your devices at all is about power. EcoFlow describes the continuous rating as the most AC power the inverter can safely supply steadily. Short spikes above it are acceptable if they stay within the surge rating, and running close to the limit for hours makes the inverter work hard and build up heat.

So check two things:

Sum of running watts (everything on at once)  ≤ continuous output (W)
Running watts of others + startup watts of the largest motor  ≤ surge output (W)

Startup (inrush) loads: fridges, pumps and motors

Appliances with motors or compressors draw much more power for a moment when they start. BLUETTI says motors and compressors can briefly draw 2–4 times their normal power. Anker says a refrigerator compressor’s startup surge can be several times its normal running wattage. By the 2–4 times rule of thumb, a compressor that runs at about 100 W could need roughly 200–400 W for a moment at each start.

If the surge is more than the power station can supply, the appliance may fail to start or the station may cut its output. The appliance’s label or manual sometimes lists starting watts or current. If it doesn’t, ask the manufacturer, or test with the power station while you’re home and can watch it.

Cycling loads: refrigerators and aircons

Refrigerators, freezers and aircons don’t draw the same power all the time. The compressor runs, rests and runs again. Anker makes the point directly: a refrigerator rated at 150 W does not necessarily draw 150 W continuously, so use its measured average consumption rather than its maximum rated wattage.

Average watts = energy used per day (Wh) ÷ 24
Runtime (hours) = rated capacity (Wh) × 0.85 ÷ average watts

You can get daily energy from a plug-in energy meter or from the steps in our guide on how much electricity a refrigerator uses. Anker adds that runtime may be shorter in warmer conditions or with frequent door opening. Both are normal in a Philippine kitchen during a summer brownout.

Aircons are harder. An inverter aircon slows its compressor down once the room is cool, while a non-inverter unit cycles fully on and off. See how much electricity an aircon uses for ways to estimate average watts. Whatever the type, an aircon’s average draw is usually far larger than a fan’s, so runtime on a portable unit will be short.

Running several devices at once

Add up the watts of everything that will run at the same time, then use the formula once. For a mix of steady and cycling loads, work in energy:

Energy needed (Wh) = Σ (device watts × hours used)
Rated capacity needed (Wh) ≈ energy needed ÷ 0.85

Then do the power check separately with the highest combined running watts, plus the startup surge of the biggest motor. Our appliance consumption calculator helps with the per-device kWh figures.

Battery chemistry: LiFePO4 vs NMC

Power station spec sheets commonly list one of two lithium-ion chemistries: lithium iron phosphate (LiFePO4 or LFP) or nickel manganese cobalt (NMC). Chemistry has less effect on a single night’s runtime than on how many years and charge cycles the battery lasts. Manufacturers make these claims:

• Anker says LiFePO4 offers 3,000–6,000 cycles, against 500–1,000 cycles for standard NMC batteries.
• EcoFlow says LiFePO4 batteries are typically rated for 3,000–6,000 charge cycles before their capacity drops to 80%.

These are manufacturers’ ratings under their own test conditions. When comparing units, read the spec sheet’s cycle count together with the capacity it ends at (for example “to 80%”), because brands state cycle life in different ways.

Temperature effects

Batteries and inverters are sensitive to heat. EcoFlow advises running a power station in a cool, dry, well-ventilated space and warns that heat buildup can trigger a shutdown and wear out the battery early. Anker lists temperature among the factors that affect runtime, and says battery lifespan depends partly on storage temperature.

In the Philippines that means:

• Don’t leave the unit in a parked car, in direct sun on a balcony, or in a closed cabinet.
• Leave space around the vents, especially when running high loads.
• Charge and use it within the temperature range in its manual.

Battery ageing

Batteries lose capacity gradually. Anker gives the example of a 1,000 Wh battery that holds only 800 Wh after enough cycles, and says a battery is usually considered aged at around 80% of its original capacity. To plan with an older unit, multiply the rated capacity by its estimated remaining health:

Runtime (hours) = rated Wh × remaining health × 0.85 ÷ load (W)

With 80% health, the 12.1-hour estimate in worked example 1 drops to about 9.7 hours. EcoFlow also advises not leaving the battery at 0% for long periods and, for long-term storage, keeping it between 20% and 80% charge.

Recharging with a solar panel

During a long outage, solar can top the battery up. Two limits apply: the panel’s output and the station’s maximum solar input. Anker defines usable solar input as whichever of the two is lower.

Usable solar input (W) = lower of (total panel rating, station's max solar input)
Solar energy per day (Wh) ≈ usable solar input × effective sun hours × efficiency
Charging time (h) ≈ battery capacity (Wh) ÷ usable solar input (W) × 1.2

The 1.2 in the last line is Anker’s allowance for real-world losses, because panels rarely keep their rated output through a whole charge. Anker lists heat, cloud cover, panel angle and shade as reasons output drops. All of these are common during the Philippine rainy season and typhoon days.

A quick runtime checklist

1. Find the rated capacity (Wh), continuous output (W) and surge output (W) on the label or in the manual.
2. List each device and its real draw. A plug-in energy meter or the power station’s display is better than the label.
3. Use average watts for cycling appliances and check their startup surge separately.
4. Use DC ports where devices allow it, and switch off the AC inverter when you don’t need it.
5. Apply 0.85, or your manual’s DoD × efficiency, and multiply by battery health for older units.
6. Keep a 15–25% margin for heat, light-load inefficiency and other surprises.

The power station runtime calculator runs these steps for you. Our guide to choosing backup power during Philippine brownouts covers whether a power station is the right tool at all.

Looking at EcoFlow units specifically? The EcoFlow runtime calculator fills in each model’s official capacity and continuous output, and the EcoFlow buyer’s guide shows estimated runtimes for every model side by side. If you buy one, signing up for a free EcoFlow account gives you 500 EcoCredits and coupon codes for your first order. You can also shop EcoFlow’s official stores on Shopee and Lazada, where marketplace vouchers apply — see how to get EcoFlow vouchers and promo codes.

The bottom line

Start with rated Wh × 0.85 ÷ load W. Several manufacturers use that formula, and it gives a sound first estimate for AC loads. Then adjust it: use average watts for fridges and aircons, check the continuous and surge ratings separately from runtime, count idle draw, and allow for heat and battery age. If the numbers only just work on paper, the unit is probably too small for your needs.