American travelers looking to bring an extra power source on a cross-country trip should now think twice about how they carry it. A new Transportation Security Administration rule says spare lithium-ion and lithium-metal batteries, including power banks and cell phone battery charging cases, cannot be packed in checked-in luggage.

TSA was jolted into action due to a safety issue with the common travel accessories. Lithium batteries can pose a fire hazard, especially if damaged. Fires in cargo holds can spread quickly and are more difficult to control than those in the cabin.

“Since they contain so much energy, lithium-ion batteries are susceptible to overheating — which can lead to a fire or explosion,” explains processing service Battery Recyclers of America.

Nervous passengers afraid of being stranded without juice will be relieved that the batteries are still allowed in carry-on luggage. Tourists can carry two spare larger lithium-ion batteries (101–160 Wh) or lithium metal batteries (2-8 grams) on board.

The regulation only applies to spare batteries. Consumer electronic items like games, tablets, smartphones, and camcorders are allowed in both carry-on and checked luggage. If you still like to make to-do lists on a Palm Pilot, no one will stop you from rolling it up with your socks.

The new rules cover a swath of handy power sources. TSA cites the following in its list of carry-on only items:

• Cellphone battery charging cases
• Rechargeable and non-rechargeable lithium batteries
• Cellphone batteries
• Laptop batteries
• External batteries
• Portable rechargers

The battery mandate was not the only change to hit airports last week. The deadline for Real ID compliance arrived on May 7. Travelers without updated identification can still fly, but should expect a lengthy TSA screening.