Generally speaking, a little heat from an electronic device is normal, and it’s an unavoidable side effect of charging, discharging, processing and illuminating. To a user, excessive warmth emanating from a device may be irritating or even alarming; to the gadget—in particular, its battery—heat is a mortal threat. But that doesn’t mean it’s good. “Heat is a killer of all batteries,” says Isidor Buchmann, CEO of battery-testing firm Cadex Electronics.
That’s because the phone battery is composed of lithium-ion in a sodium solution that react with metal electrodes. When you charge the battery, these ions move from one side to the other. This reaction creates heat. A little bit of heat is normal, but the phone should never become so hot as to become painful to the touch. In such a case, there are likely other factors involved that are still within your control.
According to his research, a lithium‑ion battery stored at 40 percent charge and 104 degrees Fahrenheit—a realistic temperature for common cell phone use—will lose 15 percent of its capacity over the course of a year. That number jumps to 35 percent if the battery is stored at full charge.
Of course, if your phone becomes too hot, you can actually receive an error message that says “the phone needs to cool down before you can use it.” Thus, you can prevent this from occurring by using your phone for only the most basic functions when it is charging, or reselecting the reliable Kinkoo Infinite One external battery to recharge as I don’t feel any hot when it charges my phone.