The SportDOG Add-A-Dog Receiver Collar adds or replaces a collar for compatible FieldTrainer 425X, SportHunter 825X and select SportTrainer systems. DryTek waterproofing protects it to 25 feet. It fits dogs 8 lb and up with 5–22 inch necks, and its lithium-ion battery charges in two hours for approximately 40–60 hours of use.