Sizing guide · checked 2026-09-03
What size portable power station do I need? A UK sizing guide
Phones and laptops: 0.288 kWh (C300 DC). Fridge plus essentials through an outage: ~1 kWh (C1000 Gen 2). Campervan or power tools: ~2 kWh and 2,400W (C2000 Gen 2). Multi-day backup: 3+ kWh (F3000). Size by output first, capacity second.
The 60-second sizing rule: watts first, watt-hours second
Two numbers decide everything. Output (watts) is what the box can run at once. A 300W box will not start a 2,000W kettle no matter how full it is. Capacity (kWh) is how long it runs: a 1 kWh box feeds a 100W load for roughly 10 hours.
List what you will run simultaneously, add the watts, add 20% headroom, and you have your minimum output. Then multiply by the hours you need, and you have your minimum capacity.
Small jobs: phones, laptops, lights
Phones, tablets, laptops, camera batteries, LED lights: all small, all intermittent. The Anker SOLIX C300 DC (£189) holds 0.288 kWh with 300W output. A phone charges ~15 times over, a laptop ~4 times, and dual 140W USB-C refills the box to 80% in an hour.
Anything bigger is dead weight in a backpack. Start here unless you have a fridge or power tools on the list.
One evening of essentials: the fridge test
A fridge draws 100–200W when the compressor runs, plus lights, router and phone chargers. Through a typical evening outage that is roughly 1 kWh, exactly the C1000 Gen 2 (£599): 1.02 kWh, 2,000W across 9 sockets, and a 10-millisecond switchover that keeps the router up.
Fridge figures vary by model and ambient temperature, so check your fridge's rating plate and add margin rather than trusting any single number.
Big jobs: campervans, tools, multi-day backup
Campervans, sheds and DIY add two demands: higher output for tools and charging on the move. The C2000 Gen 2 (£898.99) answers both with 2.05 kWh (expandable to 4 kWh), 2,400W output, a campervan socket and alternator charging while you drive.
For backup measured in days rather than hours, step up to the F3000: 3.07 kWh on wheels with up to 2,400W of solar for ~1.5-hour sun recharges. Anker reckons one charge runs a fridge about 42 hours.
Before you buy: check the money, not just the size
Sizing tells you what box you need; money tells you whether it is worth it. If you are hoping a battery saves on bills rather than covering outages, run your tariff and evening use through the savings calculator first, and read whether a battery pays without solar. Portable boxes rarely earn their keep on bill savings alone.
Questions people ask
How do I work out what size I need?
Add up the watts of everything you will run at once, then pick a box whose steady output covers it with headroom. Then check capacity: a 1 kWh box runs a 100W load for about 10 hours.
What size runs phones and laptops on a camping trip?
A phone holds around 15Wh and a laptop 50–70Wh. The 288Wh C300 DC recharges a phone roughly 15 times or a laptop 4 times. Plenty for a weekend.
How do I size a box for power cuts?
Measure one evening with a plug-in meter or your smart meter, then add margin. If the answer is under 2 kWh of essentials, a 1–2 kWh box covers it.
Will a bigger box cut my energy bills?
No. Portable boxes run appliances from their own sockets; they cannot feed home wiring. For bill savings you need a battery on a cheap tariff, so try the calculator.
Sources and further reading
- Anker SOLIX UK — C300 DC product page0.288 kWh, 300W, 140W charging, 80% in 60 min
- Anker SOLIX UK — C1000 Gen 2 product page1.02 kWh, 2,000W, 10 ms backup switchover
- Anker SOLIX UK — C2000 Gen 2 product page2.05 kWh, 2,400W, campervan socket, expansion battery
- Anker SOLIX UK — F3000 product page3.07 kWh, 2,400W solar input, 41.5 kg, fridge runtime