Keeping phones charged during a power outage

A phone uses energy mainly for three things: the screen, the radio connections and apps running in the background. Searching for a network is especially sneaky. When there is little or no reception, the phone transmits harder and keeps looking for a mast – and that drains the battery fast. So when the network is down, it can make sense to switch on flight mode and only check briefly at fixed intervals whether there is a connection again.

Energy during an outage is therefore a stock. You combine three things: stored energy (charged power banks), saving (screen, radio, apps) and – only where safe – recharging from other sources, such as the car or a solar panel.

Cold matters too. Batteries deliver less energy at low temperatures and then seem to go “flat” sooner. If you carry the phone and power bank in an inside pocket close to your body, they stay warm and last longer.

Preparation is what counts. Charge power banks fully and check them regularly, for example when the clocks change, because even unused batteries slowly lose charge. When severe weather is forecast, charge all phones, power banks and rechargeable lights as a precaution. Keep the right cable for each device at hand.

In a household, dividing roles helps: one phone stays on for emergency calls and warnings, the others are switched off and kept as a reserve. If everyone uses their phone at once, they are all flat in the end. Videos and constantly refreshing news apps use a particularly large amount of energy.

In longer outages, municipalities often set up contact points with backup power where you can charge devices. You usually hear about them on the radio or from notices. Bring your own cable and a multi-port USB plug.

The car can charge devices through a USB adapter. The danger here is not the charging but the running engine. The vehicle stands outdoors, the exhaust is clear – in winter also of snow –, nobody sleeps in it and it does not run unattended. With the engine off, avoid draining the starter battery, or the car may not start later.

Do not keep charging or using swollen, damaged or very hot batteries. Do not charge power banks under blankets or pillows, because the heat cannot escape there.

Always keep some battery in reserve for emergency calls. If the mobile network has failed completely, the municipality's contact points are the way to call for help. The emergency number is the local emergency number (112 in the EU).

Charged phones help in short and multi-day outages and also on the road after an evacuation. But they are useless if the mobile network itself fails. That is why the phone does not replace a battery or crank radio as the main source of information.

Larger battery packs, so-called power stations, can also run lamps and small devices. Crank devices with a USB output, by contrast, usually deliver only a little energy – enough for a short call, not for normal use. For medical devices: only a solution agreed with the doctor or supplier.

How long a battery or power bank lasts cannot be stated across the board. It depends on the device, the age of the battery and the temperature. Power banks also lose capacity over the years. The most honest approach is your own test: charge your phone once completely from a full power bank and see how many times that works.

Mobile masts usually have only limited backup power. That is why Ready.gov and the BBK also recommend phone numbers on paper and a battery-powered radio.