Question: I don’t fly often, but I understand that sometimes the overhead space is limited on small planes and people have to check bags at the gate. So I wasn’t surprised when the gate agent made an announcement about this when I was waiting to board my flight last week.

However, I was surprised when she said you had to remove any lithium batteries from your bag if you were going to check it. Is this some new rule? I wanted to ask the gate agent, but she was busy.

Answer: U.S. airlines haven’t allowed passengers to pack spare lithium batteries in checked bags since 2008, actually. The reason is that these batteries, while generally not dangerous, can burn at very high temperatures if they happen to ignite. I think the logic is that if that were to happen in the cabin of the plane, a flight attendant could use a fire extinguisher and put out the flames, but if a fire started in someone’s checked bag, deep in the belly of the plane, no one could get down there to fight the fire.

They make the announcement at the gate because a passenger might have, say, a spare lithium battery for a digital camera in his carry-on. That battery shouldn’t be in the bag if it’s gate-checked — the passenger should carry it onto the plane. For the record, if a lithium battery is installed in something, it’s OK in either a checked or carry-on bag; you just can’t check a loose lithium battery.

Q: My airport has a "one item only" security line. This is fairly new and always seems to move much faster than the regular security lines. I’m going to be traveling soon with my 7-year-old daughter, and I’m planning to bring my purse and one small suitcase as carry-ons. Can we get in the one-item line, since each of us would technically have one item (even if they’re both really mine)?

A: I think you can, but I’d have your daughter carry your purse as you approach the X-ray machine so it’s clear you’re each carrying one item.

Email travel etiquette questions to Lesley Carlin at deartripadvisor@tripadvisor.com.