The External Battery Pack provides additional power to your CED7000 for up to 25 hours of normal use, while charging the internal battery at the same time. The battery pack holds 2 Alkaline “AAA” batteries available in most places. You can attach the battery pack directly to the timer or connect it by an accessory cable (included), allowing the battery pack to be stored in your pocket with the timer in use on the belt clip or neck lanyard.