SportDOG TEK Series GPS Tracking Add-A-Dog Collar - The TEK-2L TEK Series GPS Tracking Add-A-Dog Collar lets you add another dog to your existing TEK Series 1.5 and 2.0 Systems. For dogs 8 pounds or larger with neck sizes 10.75in - 23in DryTek waterproof and submersible to 25 feet Up to 10 miles using HopTek technology Rechargeable lithium-ion batteries Charges in 4 hours, lasts about 24 hours per charge