Every time Apple unveils a new iOS, iPhone users seem to complain how the upgrade decimates their battery life, but part of the issue may be leaving phones plugged in overnight.

Even though phone batteries stop charging when they reach 100 percent, the charger continues to top off the battery through the night, according to Cadex Electronics communication manager John Bradshaw.

Bouncing between a full charge and just slightly below fully charged raises the phone's temperature, reducing battery capacity over time, Bradshaw told Time magazine.

“If you think about it, charging your phone while you’re sleeping results in the phone being on the charger for three to four months a year,” Hatem Zeine, founder of wireless charging tech developer Ossia, told Time. “So even though the manufacturers try their best to cover this scenario, this process inevitably lowers the capacity of your phone’s battery.”

So what's a responsible smartphone owner to do? 

Bradshaw suggests plugging phones in when the battery reaches about 35 to 40 percent since charging an empty battery puts more wear on it. Then unplug soon after the battery reaches 100 percent.

Another tip is to take off phone cases while charging to keep the temperature down since heat accelerates the loss of battery capacity.