Fenix tk75 extended runtime kit the tk75s runtime can be extended with the addition of body tube segments and battery holders an extra tk75s runtime will be gained with the addition of each extended runtime kit features install the kit with the right direction an extra tk75s runtime will be gained with the addition of each extended runtime kit the use of more than three kits in one tk75 flashlight is not recommended specifications model aer tk75 size 100mmlength52mm