How to choose a portable power station: capacity, output and price per Wh

Capacity (Wh) and output (W)

Two numbers describe every portable power station. Capacity, in watt-hours (Wh) or kilowatt-hours (kWh), is the energy stored in the battery: a 1,000 Wh unit can in principle deliver 100 W for ten hours or 500 W for two. Output, in watts (W), is the most power its inverter can deliver at once: a kettle drawing 2,000 W will not run on a station rated at 1,800 W, however large its battery.

Look at three output figures. The continuous (rated) output is what it sustains indefinitely. The surge or peak output covers the brief start-up spike of motors and compressors in fridges, pumps and power tools. Many brands also offer a boost mode that runs resistive loads such as heaters above the rated output by lowering the voltage; useful, but it does not suit electronics or motors.

Sizing it to your needs

1. Peak load. List what must run at the same time and add up the watts. The continuous output must exceed it, with headroom for any motor's surge.
2. Energy. For each device multiply watts by hours of use, then add them up. A device's watts are on its label or power adapter.
3. Losses. Converting battery power to AC costs energy, and stations keep a reserve to protect the battery. Plan on about 80% of the rated capacity reaching AC appliances; DC and USB outputs lose less.

An example: a home office during a power cut, with a 60 W laptop, a 15 W router and a 25 W lamp for eight hours, needs 100 W × 8 h = 800 Wh, so about 1,000 Wh of capacity after losses. Add a fridge and you need both more energy and enough surge for its compressor, which puts you in the 2 – 3 kWh class. Whole-home backup for a day, including heating or air conditioning, calls for an expandable system of 5 kWh and more, or a home battery.

LFP or NMC battery

Most current models use LFP (lithium iron phosphate, LiFePO₄) cells; older and lighter ones use NMC lithium-ion. The difference is mainly lifespan. Goal Zero, which sells both, specifies its LFP Yeti battery packs for 4,000 cycles to 80% capacity and its NMC Yeti 6000X for 500. EcoFlow quotes more than 3,000 cycles for the LFP DELTA 2 Max. LFP is also more tolerant of heat and abuse. NMC packs are lighter for the same capacity, which matters for a unit you carry by hand, but for backup and daily solar use LFP is the better choice.

Charging: wall, solar, car

• Wall charging speed is now a selling point: many 1 – 2 kWh units charge from the mains in about an hour.
• Solar input is limited by watts and by voltage range. To recharge 2 kWh in a day of sun you want 400 – 800 W of panels, and the station's solar input must accept that.
• Car charging through a 12 V socket is slow (around 100 W); alternator chargers that connect to the car battery are much faster for vans and RVs.
• Pass-through and UPS. If the station powers devices while plugged in, check its switch-over time: a few milliseconds keeps computers and routers running through a power cut.

What each size costs

Median store price of stand-alone power stations in PowerTrusted's library, by capacity. Bundles with panels or extra batteries are excluded.

Small units cost far more per watt-hour, because the inverter, case and electronics weigh more in the price. Above about 2 kWh the price per watt-hour levels off. Prices change often with promotions; each product page shows the current store prices.

Certification and recalls

In the United States, look for a listing to UL 2743, the safety standard for portable power packs, from a recognised testing laboratory; the listing mark names the laboratory and a file number you can check. Every lithium battery must also pass UN 38.3 transport tests. Units that will be permanently wired into a home as an energy storage system fall under UL 9540. Recalls happen even at leading brands; each brand's page on PowerTrusted lists the recalls issued by the US Consumer Product Safety Commission and the EU Safety Gate.

Models compared

Stand-alone power stations with stated capacity and a current store price, from smallest to largest:

All 827 products, including bundles, expansion batteries and panels, are in portable power stations.