Portable Power Station Runtime Calculator

Work out realistic portable power station runtimes for any appliance, with usable energy, losses and inverter limits.

Most runtime calculators divide watt hours by watts and stop there. That maths is optimistic, and it is why people end up surprised when their power station runs flat hours earlier than the number suggested. This calculator accounts for the two things that quietly eat your runtime: inverter losses when you draw from the AC sockets, and the reserve you should leave in the battery to protect its lifespan. What you get is a figure far closer to what you will actually see in a tent, a van or a power cut. WHAT IT WORKS OUT Enter your battery capacity, the wattage of your appliance and how you are drawing power, and the calculator returns: - Estimated runtime in hours and minutes - Usable battery energy in watt hours, after losses and reserve - Estimated energy loss in watt hours - The reserve and efficiency figures used in the calculation - A visual gauge showing how much of the nominal capacity is genuinely usable HOW THE MATHS WORKS usable energy = capacity x efficiency x ((100 - reserve) / 100) runtime = usable energy / appliance watts Efficiency depends on how you take the power. AC output runs through the inverter, so you choose an efficiency between 80 and 95 per cent. DC output is fixed at 95 per cent because there is no inverter in the path, only DC to DC conversion loss. USB output is fixed at 90 per cent to account for regulator loss. Most people should leave AC on 85 per cent, which is a fair figure for the units sold in the UK. Worked example. A 1024Wh unit running a 60W laptop from the AC socket, at 85 per cent efficiency with 10 per cent held in reserve, gives 783Wh usable and a runtime of 13 hours 3 minutes. Straight division would have told you 17 hours. BUILT IN APPLIANCE LIST Fifteen common loads with typical wattages, so you do not have to go hunting for a figure: laptop, phone charger, router, Starlink, CPAP machine, LED TV, mini fridge, fan, microwave, camera charger, drone charger, games console, coffee machine, projector and electric blanket. Tap one and the wattage fills itself in. QUICK PRESETS Six scenarios that highlight the appliances people typically run: Camping, Home Backup, Caravan, Photography, Emergency Kit and Remote Working. SAFETY WARNINGS The calculator flags when an appliance draws more than your power station's inverter can safely deliver, which is the mistake that catches people out with kettles, microwaves and coffee machines. The inverter limit scales sensibly with the capacity you pick, and you can edit it to match your actual unit. It also tells you when a runtime is short enough that you probably want a larger battery. OTHER THINGS IT DOES - Light and dark modes - Remembers your settings between sessions - Copy, print, save as PDF or share your results - Works completely offline - Keyboard accessible, with screen reader support and WCAG AA colour contrast PRIVACY The calculator collects nothing. No accounts, no analytics, no tracking, no network requests of any kind. Your settings are stored locally on your own device so the tool remembers them next time, and they never leave your machine. The only permission it requests is local storage, which is what makes that possible. ABOUT US Built by the team behind portable-powerstation.co.uk, a UK site reviewing portable power stations and off-grid kit. We do not make fake hands-on testing claims. We work from manufacturer specifications, hundreds of UK Amazon and Trustpilot reviews and professional teardown analysis, with a focus on what matters here: sterling pricing, UK warranty support, three pin sockets and British weather. The figures this calculator produces are estimates. Real runtime varies with battery age, temperature, appliance start-up surge and how the manufacturer rates capacity. Treat the result as a well-informed planning figure rather than a guarantee.