Why the battery runs out faster on a trip, and what actually helps

Ask the phone first: it often tells you

On an iPhone, open Settings › Battery and scroll to the list of apps and system activity. Apple explains the notes that can appear under each one, and one of them is Cellular coverage: the app was used in a low-signal environment, which used more battery. Apple's battery tips page says the same about its Low Signal message, which means the phone has been in poor coverage searching for a better signal.

On a Pixel, Settings › Battery › Battery usage shows what used the most, and on a Pixel 6 or later Settings › Battery › Battery diagnostics has an option for a battery draining too quickly. If the top of the list is navigation, the camera or a video app, the cause is how you used the phone. If nothing stands out and you spent the day on trains and ferries, the culprit is probably the signal.

Searching for signal is the hidden cost

A phone in weak coverage keeps raising its effort to hold on to a network or to find a better one, and it does that whether you are using it or not. Mountain railways, ferry crossings, rural roads and the inside of thick old buildings are the typical places. Apple's advice for low-signal areas is direct: turn on airplane mode. You will not make or receive calls while it is on, so it suits a stretch with no coverage anyway, not a day in the city.

Two lines double the job. With your usual SIM and a travel eSIM both active, each keeps its own connection, with its own row of signal bars. A Snoozim country pack only works in its own country, so when you cross a border with it, switch that line off until you are back: it has no network to find. Switching a line off is not deleting it, and it comes back with one tap.

Maps, camera and a bright screen

Google's list of what drains a Pixel fastest reads like a holiday: long navigation sessions, video, the camera, graphics-heavy games, streaming and long GPS use. None of it is avoidable on a trip, but some of it can be shortened. Download offline maps so the phone is not fetching map tiles over a weak connection, as in the guide to Google Maps offline, and lock the screen between turns instead of keeping navigation on full brightness.

Google also suggests turning down brightness, a short screen timeout and turning off Bluetooth when you are not using it. Battery Saver on a Pixel turns off most location use and most automatic syncing, which is often what keeps the phone busy in a pocket.

Power modes worth switching on early

• iPhone: Settings › Battery › Low Power Mode, or Settings › Battery › Power Mode › Low Power Mode on iPhone 15 and later. It switches itself off once the phone charges to 80%.
• iPhone 15 Pro and later: Adaptive Power, on by default on supported models, can turn on Low Power Mode by itself at 20%.
• Pixel: Battery Saver, or Extreme Battery Saver when the battery is about to die. Google notes that Battery Saver turns off 5G.
• Both: switch off the hotspot when nobody is using it.

Turn the power-saving mode on in the morning of a long travel day rather than at 10%: it is far more useful stretching a full battery than rescuing an empty one. On an iPhone, the default 5G Auto setting already drops to LTE when 5G would not make a noticeable difference, to save battery, while 5G On may reduce battery life.

Heat, cold and charging on the road

Apple gives the comfortable range for its devices as 16 to 22 °C and warns that ambient temperatures above 35 °C can permanently damage battery capacity, with charging in the heat making it worse. A phone left on a sun lounger, a car dashboard or a window ledge on a summer afternoon is in exactly that situation. Google adds that heat drains the battery faster even when the phone is not in use.

Cold is different: Apple says the drop in battery life in very cold conditions is temporary and recovers when the battery warms up. On a ski day, a pocket close to your body keeps it working. Google also recommends using the charger that came with the phone, since others may charge slowly or not at all, which is worth remembering before buying a cheap one at a station kiosk.