Wii Energy Pak for Wii Balance Board Rechargeable lithium-ion battery pack - up to 30 hours of play time per charge. Unique AC port relocator allows easy charging of the battery pack. Play and charge simultaneously. Detachable AC cord for wire-free play. Plugs into any wall outlet - faster charge than USB. Battery pack conveniently charges while inside the Balance Board - no need to remove it once it is installed Convenient LED charge / battery indicator