Replacement battery fits 11 Petsafe compatible models. Specifications: 150mAh, 3V, Li-MnO2. Compatible with: A12, R-21, R-51, Invisible Fence R21, Invisible Fence R22, Invisible Fence R51 and 5 more compatible models. Replaces: PetSafe RFA-182, Invisible Fence IFA-001. Petsafe replacement battery designed for Dog Collar devices. Designed for long-lasting power.