1) Using chargers for your iPhone that aren't from Apple.
“This can go for both the USB wire and the USB adaptor plug,” Wilkes says. “Using either the wrong wire or plug can severely damage your battery. In a lot of cases they will charge your device with the incorrect voltage (either too high or too low will damage the battery). Although they may be overpriced, stick to the chargers provided by Apple.”
2) Overcharging your device.
“Whilst not as big of an issue with the most recent iPhones, keeping your phone on charge after it hits 100% can damage the battery as it 'trickle charges' it,” Wilkes says. “This is basically your phone stopping any charge going to the battery once it hits 100%, then once it falls to 99% it tops it back up. Doing this over and over until you take it off can overheat the battery, causing (a slight amount of) permanent damage.”
3) Overheating your device.
“This can be done in a number of ways, some phones overheat when you use an intensive app or game and all phones of course overheat if they're left laying out in the sun,” Wilkes says. “Keeping your iPhone at room temperature can drastically improve its battery life.”
4) Contrary to popular belief - it's much better to avoid letting your iPhone die.
“Keep [your phone] at least partially charged (Anything above 0%),” Wilkes recommends. “Whenever your battery is draining, your are essentially restructuring the electrodes in the battery, the less it discharges, the less it restructures.”
5) Using fast chargers on phones not designed for them.
“The majority of new iPhones are built to handle fast chargers,” Wilkes says. “However, if they're not you run the risk of damaging your battery, again, due to heat.”
Keeping these tips in mind the next time you charge your device — and making changes where necessary — can ensure that your phone’s battery continues to run efficiently, saving you a ton of money in the long run.