There’s much talk about how overcharging your phone or allowing it to drop below a 10 percent charge is bad for your phone’s battery. But where you physically rest your phone during a charging session should also be a consideration. “This is an unusual but TRUE fact about draining the battery of a phone,” Perrett says. “Leaving your phone on a non-flat surface (such as your mattress) drains the battery overnight.”
As it turns out, leaving your phone to charge on your bed, pillow, or couch, as you might instinctively do before getting ready for sleep, is a mistake. Doing so traps heats inside of your device and can result in it overheating.
When your phone overheats, this also causes potential damage to its Lithium-ion battery. Similar to the way you are advised not to charge your phone in extreme temperatures — whether that means in a hot car or on a ski slope — the same rule applies when it comes to charging your phone on non-flat surfaces.
Maintain your iPhone battery by providing it with occasional charges throughout the day, which prevents it from dipping below 20 percent. And if you choose to charge it overnight, avoid tossing it on a bed or sofa and do so on a nightstand or dresser table, which is far better for the health of your battery.