Power pack
From Tardis Wiki, the free Doctor Who reference
Power Packs were a common form of generating power. They were similar to the Earth batteries. When Nyssa found a number of power packs in London, it proved the crash must have been light and passengers may have survived as the power packs were fragile. The Terileptils used them to power their mind controlling bracelets. They were easily removed however, quickly disabling the mind control capabilities. (DW: The Visitation)
