The SportDOG Brand® SD-425X X-Series Add-A-Dog® is the collar receiver for the FieldTrainer® 425X and SportHunter® 825X Remote Trainers. If you’re looking to add another dog to your current SportDOG Brand® electronic collar system look no further. This collar receiver is the perfect addition or replacement to your collar system. FEATURES: Collar receiver only Operating guide included Includes collar receiver on strap Long contact points for longer haired dogs Charging adapter for convenience Rechargeable lithium-ion batteries with 2-hour quick charge Waterproof and submersible up to 25 feet using DryTek® technology For dogs 8 pounds or larger with neck sizes 5 to 22 inches wide