The 500-CARRIER makes it possible to replace the TAC-410XL / TAC-460XL / TAC-510XL / TAC-540XL / TAC-560XL / TAC-660XL rechargeable battery, with 2 non-rechargeable CR123 batteries. If the rechargeable battery on the TAC-400/500/600 Series lights were to run down, the user could insert a pair of CR123 Lithium Metal batteries into the carrier and then use it in place of the rechargeable battery. Requires 2 CR123 Batteries which are not included. (Not compatible with CR123-style rechargeable batteries.)