Batteries wear out, but habits change how fast. Only the practices with evidence behind them.
Lithium-ion cells age fastest when drained near 0% or held at 100% for long. Frequent small top-ups between 20% and 80% are kindest to lifespan. The 'optimised charging' or '80% limit' setting on modern phones automates exactly this — leave it on.
Temperature affects ageing more than anything else. Gaming while charging, leaving the phone in a hot car, or fast-charging inside a thick case all build heat. If it feels hot while charging, take the case off and keep it out of direct sun.
The display is the largest daily drain. Auto brightness, a short screen timeout and dark mode (only on OLED) make a real difference. Trimming background refresh and location permissions per app cuts idle drain too.
'Resetting' a battery by fully draining it dates from nickel batteries; it harms lithium-ion. Third-party chargers that meet the spec are fine, but avoid ones that run hot or list no output rating.
How far a battery has aged is better judged by numbers than by feel. Many smartphones show maximum capacity or battery health in the settings, usually as a percentage of the original capacity; once that drops a lot, getting through a day becomes difficult with the same use. Where the menu is and how it is displayed differ by manufacturer and system version, so check the maker's guidance. If battery life suddenly gets much shorter, one app draining power is often the cause rather than ageing, so look at usage by app first.
For a spare phone or tablet left unused for months, how it is stored decides how long the battery lasts. Leaving it at 100 percent or completely empty both stress the battery. The commonly recommended approach is to charge it to about half, power it off and keep it somewhere cool and dry. Batteries slowly self-discharge even when off, so take it out every few months and top it back up to around half. Left too long, a fully drained battery may refuse to turn on again.
A swelling battery can lift the screen, bulge the back or make the phone rock on a table. If you see this, stop charging and stop using it. Pressing it back down or opening the phone to swap the battery yourself is dangerous, so take it to an official service centre. If the phone becomes too hot to hold while charging, or you notice a burning smell or smoke, unplug it immediately and move it away from anything flammable. If it catches fire, keep away, get out and call emergency services. Avoid charging overnight on a bed or under bedding, where heat cannot escape.
Batteries wear out no matter how carefully you treat them. If you always need a power bank to get through the day, or the phone keeps shutting down while it still shows charge left, it is time to consider a new battery. When the phone itself is still fast enough, replacing only the battery is often far cheaper than buying a new phone. Have it done at an official service centre or authorised repair shop; non-genuine batteries vary in quality and safety. Cost and availability differ by model, so ask in advance.