The settings that really matter
| Setting | Real gain |
|---|---|
| Low power mode | High. Limits performance and background tasks, activatable below 20% battery or manually. |
| Screen brightness | High. The screen remains one of the biggest power drains; lower it to the minimum readable level. |
| Bluetooth and Wi-Fi | Medium. Turn them off if unused, they search for connections continuously. |
| Vibration | Small but real. Vibrations consume more than a short ringtone. |
| App location access | Medium. Set to "while using the app" rather than "always". |
The case of airplane mode
Airplane mode cuts off all network connection, saving a lot of battery — but it also cuts off receiving FR-Alert alerts and incoming calls. It's only relevant if you're not expecting a call or an urgent alert, for instance during a long journey where you know you won't be reachable anyway. When in doubt, prefer lowering brightness and closing unnecessary apps rather than cutting off the whole network.
Charging without electricity
- Power bank: the most reliable solution, provided it's charged in advance. Make it a reflex item in your emergency kit.
- Car charger: useful if a car remains accessible and functional.
- Portable solar panel: a backup option, whose output depends heavily on sunlight and isn't guaranteed in bad weather.
Prioritising uses
In an emergency, the phone replaces several objects at once: flashlight, radio, alert method. Prioritise in this order:
Receiving official alerts
Keep the network active for FR-Alert and incoming calls.
Contacting relatives
A text rather than a call, see our guide on communicating without network.
Everything else
Social media, browsing, entertainment: the last things to keep as battery runs low.
Mistakes to avoid
- Leaving the screen on continuously to check the news every minute.
- Switching to airplane mode while waiting for an important call. You'll never receive it.
- Relying on a power bank that's never charged. Check it at the same pace as the rest of your emergency kit.
- Using the phone for entertainment while battery is still uncertain.
Seeing your relatives' battery
LASTLINE can help you:
- see the battery level of household members who've shared their status;
- send an SOS that includes your battery level, so your relatives know how long they can reach you.
LASTLINE doesn't charge your phone: keep a charged power bank in your kit.
See my household's statusFrequently asked questions
Should you switch your phone to airplane mode to save battery?
Only if you're not expecting a call or an urgent alert: airplane mode also cuts off FR-Alert and incoming calls. A safer compromise is often to lower brightness and close background apps rather than cutting the whole network.
Does low power mode really slow down the phone?
Yes, slightly: it limits certain performance and background features to extend battery life. In an emergency context, this trade-off is worth it.
How do you charge a phone without electricity?
A power bank charged in advance remains the most reliable solution. A car charger lets you charge from a vehicle. Some portable solar panels exist, but their output depends heavily on sunlight.
Sources
- FR-Alert (SGDSN / Ministry of the Interior), Frequently asked questions (airplane mode and alert reception).
- Apple and Google manufacturer documentation on battery management (generic settings, not model-specific).