SportDOG Brand HoundHunter 3225 Add-A-Dog Collar - Additional, Replacement, or Extra Collar for Your Multi Dog Remote Trainer - Waterproof and Rechargeable with Tone, Vibration, and Shock This is the SDR-AH Collar Receiver only; compatible with the SportDOG Brand HoundHunter 3225 (SD-3225) The SportHunter 3225 Remote Trainer can be expanded to train up to 6 dogs with the same Remote Transmitter with the purchase of this SDR-AH 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 charge in 2 hours and last 40-60 hours per charge; features a low battery indicator to let you know when to charge