A new U.S. Department of Transportation air travel regulation that came into effect yesterday may require some to leave their laptop batteries at home. According to the DOT's Safe Travel sub-site, folks who travel by plane are no longer allowed to take spare lithium batteries in their checked luggage. Lithium batteries installed inside a device are okay with two exceptions: lithium-metal models that contain more than two grams of lithium are forbidden in all types of luggage, and lithium-ion models with more than eight grams of lithium-equivalent content are restricted in number. To help travelers wrap their head around the new rules, the DOT's Safe Travel page has a guide table with a list of allowed and forbidden batteries depending on luggage types.