I had an iPhone 4s, bought in 2011. It was always used correctly without any problems or drop. In 2015 I had another phone, I didn't charge the iPhone 4s and left it behind. Some months later it doesn't turn on. I've changed a new cable, it doesn't charge too, no screen at all. I also had a decent portable charger (MOMAX) that was not often used. In less than half year of time it gone bad totally. Luckily it was within warranty Does this example suggest that electronic parts need to be turned on and let it run sometimes let it ''exercise'' a little bit??