For most of us, this won't be a problem. But anyone heading off on a long expedition using pro-video cameras or laptop sized coms with external batteries ought to be aware.
The US Department of Transportation will allow only two of lithium batteries on aircraft if they weigh 8g-25g, and then only in cabin-baggage. Over 25g are not allowed at all.
It's to cut the fire risk. Anything with a lithium battery inside it and weighing under 8g is fine. So normal camera, mobile phones etc. are OK if they're installed. They're not allowed loose in checked baggage.