HQRP (4-Pack) Replacement Battery Cell for Power Cap Invisible Fence R21, R22, R51, MicroLite Receiver Collar + HQRP Coaster HQRP&reg; Battery (4-Pack) plus HQRP&reg; Coaster; Battery Voltage: 3V; Capacity: 160 mAh; Lithium; Each lasts 2-4 months; 60 Days warranty!