Not a problem in America, but if you're going through the Beijing airport, they will take it....at least they were confiscating them in April.
Just read about this today. It was a very long post on a website that specializes in providing information about rechargeable batteries. The poster got into the construction and chemistry. It was a LONG post. If I had had time I might of read it. (I like that kind of stuff.) For purposes of why there is a concern: If lithium ion batteries get "cold enough" they can be permanently damaged and even become dangerous. Once they warm up they can catch fire, explode, etc. Cargo holds get very cold. So batteries in them may be damaged if not well enough insulated. (If you want more info look up Filter Joe. He's into baseball too.)
Typically cargo holds on large airplanes are heated/kept somewhere between 7 to 15°C (45°F+) because checked baggage often contains liquids that would otherwise freeze, except the area where bulk items and pets are stowed which can be heated even further anywhere between 16 to 25°C if needed for pets or cold sensitive bulk cargo. And yes, the baggage compartment is pressurized just like the passenger cabin (to approx 8000' ASL equivalent) - the pressure is exactly the same as in the passenger cabin. Worst case cold to warm scenario would be baggage sitting outside for a long time in extremely cold temps before being loaded on the plane, then warming up in the cargo hold. As others noted, the reason rechargeable lithium batteries are required to be in the passenger cabin is that they can be accessed and extinguished if they short circuit internally and catch fire. Most airlines' flight crews are trained in procedures and have containment bags/devices on board in case of battery fires.
Last edited by 4eyedbuzzard; 01-14-2019 at 23:09.