SportDOG Brand FieldTrainer 425/SportHunter 825 Add-A-Dog Collar - Additional, Replacement, or Extra Collar for Your Remote Trainer - Waterproof and Rechargeable with Tone, Vibration, and Shock This is the SDR-AF Collar Receiver only; Compatible with the SportDOG Brand FieldTrainer 425 (SD-425) and SportHunter 825 (SD-825) The FieldTrainer 425 and SportHunter 825 Remote Trainers can be expanded to train up to 3 dogs with the same Handheld Transmitter with the purchase of this SDR-AF Add-A-Dog Collar Features DryTek technology making this collar waterproof and submersible to 25 feet; Fits dogs 8 pounds or larger with neck sizes 5"-22" Rechargeable lithium-ion batteries charges in 2 hours and lasts 40-60 hours per charge. Features a low battery indicator to let you know when to charge Detailed operating guide and a locally based Customer Care Center, available 6 days a week, provide support when you need it By designing our products in the field, with heat, cold, rain, snow, dust, mud, and wind in mind, SportDOG has become the most recognized brand in the electronic tracking and training categories, making the promise to always create "Gear The Way You'd Design It"