Battery-powered devices, such as laptops, tablets, and smartphones, are not allowed in checked luggage on airplanes because of the potential risk of a fire. Lithium-ion batteries, which are commonly used in these types of devices, have been known to overheat and catch fire. When a device is placed in checked luggage, it is not visible and may not be noticed if it starts to overheat or catch fire. This can lead to a fire in the cargo hold of the airplane, which could potentially cause serious damage or even a crash.

To minimize the risk of a fire, most airlines and the International Air Transport Association (IATA) have implemented guidelines that prohibit the placement of lithium-ion batteries in checked luggage. Instead, these devices must be carried on board the airplane and placed in carry-on baggage or in a personal item, where they are easily accessible and can be monitored for any signs of overheating or fire.

Additionally, it is important to note that many airlines have restrictions for lithium-ion batteries such as a maximum capacity or the need to be protected against short-circuiting. Also, many countries have regulations on the amount of lithium batteries you can carry with you, so it's always best to check with your airline and destination country before you travel.