Defibtech’s battery technology is nothing short of brilliant! A replaceable 9-volt battery powers the device’s regular electronic self-tests leaving the pack available for any emergency use. This “high-capacity” pack is ideal for environments which may require additional shock capacity. It’s another great innovation from Defibtech. If you don’t need a high-capacity battery, check out the standard battery pack instead. The AED Superstore® has them both! The Defibtech brand AEDs operate on batteries only. Always have a fully charged spare.