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Power outage planner: how long will your stored power last?

For a power outage, which some countries call a power cut. Say what you have and what it must run. You get a range, the sum behind it and the source of every figure.

Your stored power

The mAh or the Wh printed on it. If it shows both, choose Wh: the sum is then closer.

Days to cover

We start at 3. It is our starting value.

What it must run

Phones

Leave it empty to use the range of the phones we read: 3,561 to 6,000 mAh. Your phone's own figure is usually in its maker's specifications.

We start at 1. It is our starting value.

Laptops

Nothing you type here is stored or sent. The sum runs in your browser.

By this sum

Enter the size of your power bank or power station to see the sum.

Where each figure comes from

We read each figure on the maker's own page or on an official page on 12 November 2026. A range is the lowest and the highest of the figures shown under its heading. It is not every product on sale.

From mAh to Wh

Watt-hours are volts multiplied by amp-hours. In the figures under this heading, each 1,000 mAh holds between 3.65 and 3.91 Wh. That figure is the nominal voltage of the cell. The highest figure is a phone's battery, and the others are for power banks. If your power bank prints its Wh, use that figure.

What a power bank gives out

A power bank loses energy when it raises its voltage for the outlet, as Anker says below. Among the makers' figures under this heading, the share of the stored energy that reaches the outlet is 74% to 87%. Your own power bank can be outside this range.

What a phone or laptop keeps

A phone or laptop also loses energy while it charges. One maker gives a figure: 80% to 90% reaches the battery. We found no second maker who prints one.

What a power station's outlet gives out

The outlet that works like a wall socket loses energy too. Makers give 80% to 95% of the stored energy for it. We use the same range for its USB outlets. EcoFlow says below that those often last longer, so for them the sum is a cautious one.

Phone batteries

3,561 to 6,000 mAh among the phones we read. Your own phone can be outside this range.

Laptop batteries

50 to 100 Wh among the laptops we read. Your own laptop can be outside this range.

Figures we do not give

For a router, a lamp, a radio, a fridge and a medical device we give no range. We found no official typical figure that fits every market, so the sum uses only the figure from your own device's label. For a radio, the sum also uses the mAh to Wh range and the charging share that it uses for a phone. That is our choice: the maker's charging figure is for a phone or laptop. The rows below show the kind of figure that makers and official bodies print.

A fridge's energy use for a year: what official texts say

Our own starting values

3 days and 1 full charge a day are ours, not a source's. Change both.

A medical device: read this first

This is only arithmetic with the figures you gave. It is not a run time for your device.

Before you rely on stored power, confirm the run time with the maker of the device and with the company that supplies it. Ask them which battery or power station is safe to use with it.

Tell your electricity company that someone at home uses medical equipment that needs power. For some countries, an official line on this page says how.

What official bodies say

What makers say

Spotted an error?

Makers change their pages, and we can misread. Email hello@emergencykitplan.com with the figure and the source, and we will read it again.

Last reviewed: 12 November 2026.