Effective January 1, the FAA implemented new rules concerning lithium-based batteries in checked baggage. According to this Yahoo! Tech column, installed batteries and spare batteries are treated differently. Travelers will no longer be allowed to pack spare batteries in checked baggage, but they may check equipment with batteries installed. In carry-on luggage, passengers can pack as many batteries as they want, as long as they contain less than 8 grams of lithium each. In addition, travelers can bring two spare batteries with a total lithium content of 25 grams. The FAA suggests packing spare batteries in plastic bags. For additional guidelines and details, go to the DOT website.