Free tool

Power cut planner

Add the devices you would want running in a power cut. The planner adds up the watt-hours and shows how long your battery lasts, with every step of the maths.

Plan your power

Your devices

Starting figures are typical, check your device's label or charger. Choose how you want to measure each one.

    Add a device

    Your power station

    You never get the full rated capacity. Converting battery power to mains (the inverter) and the battery's own protection lose some, so 85% is a fair starting guess.

    Solar panel (optional)

    2 hours is a rough UK estimate. Winter can be well under 1, a bright summer day more. Panels rarely deliver their full rating, so treat the solar figure as a best case.

    0Wh needed per day

    0days on the battery alone

      Add up the watt-hours (Wh) each device uses in a day: watts multiplied by hours of use. Multiply your power station's capacity by about 85% for inverter losses, then divide by your daily Wh to get the number of days. A 300 Wh station running a 5 W lantern, a phone and a radio typically lasts several days.

      Questions people ask

      How long will a 300 Wh power station last?

      About 255 Wh is usable after typical losses. Divide that by what your devices use per day. A lantern for 5 hours (25 Wh), one phone charge (15 Wh) and a radio for 4 hours (8 Wh) use 48 Wh, so roughly 5 days.

      Why can I not use the full capacity of my power station?

      Converting battery power to mains through the inverter wastes some energy as heat, and the battery keeps a small reserve. 80 to 90% usable is common, so the planner starts at 85%.

      Can a solar panel recharge a power station in the UK?

      Yes, but slowly in winter. The planner multiplies the panel's watts by good sun hours, starting at 2 hours a day as a rough UK estimate you can change.

      Can a power station run a fridge?

      A fridge-freezer can use several hundred Wh a day, which drains a small power station in well under a day. It is usually a job for a generator or a large battery.

      Estimates only. Check your own devices and labels. In an emergency, always call 999.