Overcharging, overheating or even hidden manufacturing flaws can trigger a dangerous chain reaction in a lithium-ion battery known as thermal runaway, causing its internal temperature to rise.

Summer vacations are here. But if you're flying with Southwest, you need to be aware of a new rule for portable chargers.

The TSA noted that flight crews have been trained to recognize and handle battery fires that could occur in an airplane cabin. Passengers should notify the flight crew immediately if they notice a battery or electronic device is overheating, expanding, smoking or burning.

However, a new rule announced by the TSA in February might cramp your style: lithium battery-powered portable chargers and power banks are no longer allowed to be packed in a checked bag.

Here's what you can and can't pack in your carry-on and checked luggage, according to the TSA's official list.