Smartphone owners should think twice about stuffing the devices into their pockets, says a German consumer affairs group. That's because the lithium-ion batteries found in most smartphones are sensitive to heat. Anything over 35 degrees Celsius can diminish their life-span, says Tuev Rheinland.
Body heat is higher than that. Add the heat build-up when the device is using a public network on a hot day: The battery is almost bound to deteriorate.
Air circulation is what keeps a smartphone cool. Similar warnings apply to laptops, which can overheat if they don't get any cool air into their housing. That's why laptops shouldn't be used while resting on soft pillows or a lap.
Building on that, keep all the devices well away from radiators and other hot objects. Those are killers for the lithium-ion batteries.