Two numbers answer different questions
- Wh or kWh capacity
- How much energy the battery is rated to store. It helps estimate duration, after allowing for losses.
- W continuous output
- How much power the station can supply at one time through the chosen output. Add loads that might run together.
- W starting or surge output
- A short-duration limit that may matter for equipment with a motor or compressor. Check the exact appliance and station instructions.
Make a small load plan
- Choose essential uses
Start with lighting, phone charging and any communications equipment that has a useful backup purpose. Leave out heating and cooking loads unless you have checked their actual demand and a suitable arrangement. A power bank may be enough if phones are the only requirement.
- Find the watts
Use a device label, manufacturer documentation or a suitable plug-in meter for the actual device. A label may state a maximum rather than typical use, and a cycling appliance can vary substantially over time.
- Calculate energy
For each steady load, multiply watts by hours used to estimate Wh. Add all loads over the planned period. For a cycling load, use measured energy over a representative period if possible rather than treating its rated watts as a constant.
- Check output and usable energy
Compare simultaneous running watts and any startup demand with the station's stated output limits. Then compare required Wh with the maker's usable-output information, allowing room for inverter losses, standby use, battery condition and uncertain run times.
An illustrative energy budget
Suppose a router setup draws 12W for eight hours and a light draws 10W for four hours. The arithmetic is 12 x 8 = 96Wh plus 10 x 4 = 40Wh, so 136Wh for that day. For two identical days, the load total is 272Wh before station losses or other devices. These watts are examples only. Measure or verify your own equipment before choosing capacity.
A station labelled 300Wh is not a promise of 300Wh delivered at an AC socket. Its inverter and electronics consume energy, and the usable amount depends on the load and output used. If there is no trustworthy output figure for your conditions, leave a generous margin and be prepared to shorten use. Do not treat a calculated runtime as a guarantee.
Check how the equipment connects and recharges
Check the socket or DC port type, voltage, per-port limit, combined-output limit and cables in the exact station manual. If an appliance has a motor or compressor, confirm its starting requirement against the station's genuine surge rating. A short peak rating is not the same as continuous power.
Think about weight, storage position, charging time and how often you would use the battery. A larger unit may be poor value if a charged phone, power bank, torch and printed contact list already meet the main need. Solar charging adds weather and equipment dependencies and should not be assumed in a no-sunlight runtime plan.
Use the station as its maker intends
Follow the exact product manual for charging, ventilation, placement, output limits and approved connections. Keep the unit dry and away from heat, and stop using it if damaged or abnormally hot. Do not improvise a connection to the home's fixed electrical system. Ask a qualified electrician about any proposed fixed backup arrangement.
When this guide is insufficient
This is a sizing method for ordinary portable loads, not a guarantee of appliance operation or safety. Fridges cycle and may need extra starting power; food safety requires separate official guidance. A powered medical or care device needs a plan agreed with its supplier and clinical or care team. Powering a home router does not prove that the external broadband network will remain available.
Products that may help
Specific options, with the limitations visible.
These are affiliate links. The recommendation is based on suitability and evidence, not commission.
EcoFlow DELTA 3 Classic portable power station
EcoFlow DELTA 3 Classic, 1024Wh, UK model EFDELTA3C-UK-CBox-L
A rechargeable 1kWh-class power station for households that need an AC output without running a fuel generator. Check appliance demand and expected duration before buying.
- Useful for
- A household whose measured essential loads and planned duration call for around 1kWh of rated storage and up to 1800W rated AC output.
- Probably not for
- Someone who only needs occasional phone charging, cannot manage a 12.1kg unit, or needs guaranteed multi-day running.
- 1,024Wh rated capacity offers more storage than compact units.
- 1800W rated AC output supports more compatible loads.
- Official UK-model listing identifies the exact variant.
- Usable AC energy is lower than rated capacity.
- 12.1kg makes this less easy to move.
- This Classic model is not expandable.
Size the system from measured wattage and energy use, including start-up demand. Do not connect it to household wiring without qualified electrical advice.
EcoFlow RIVER 3 Plus portable power station
EcoFlow RIVER 3 Plus, 286Wh, 600W
A compact rechargeable AC power station for modest, compatible household loads where a small battery is enough. Work out the energy needed before buying.
- Useful for
- A household with measured, modest loads such as phone charging, small lighting or a compatible router supply.
- Probably not for
- A household expecting long fridge runtime, heavy appliances, or assured support for medical equipment.
- 286Wh rated capacity and 600W rated AC output provide a step up from a USB power bank.
- 4.7kg is easier to move than a larger 1kWh station.
- Can accept a compatible solar input within the stated limits.
- Usable AC energy is lower than 286Wh.
- 600W output and 286Wh capacity are separate limits.
- No verified runtime for any particular appliance.
- Solar input rating does not guarantee real-world generation.
Confirm the exact appliance power and start-up demand. Do not use as an assumed fridge or medical backup. Follow EcoFlow instructions for charging, storage and ventilation.