Perimeter Technologies saves you money with your compatible batteries for Invisible Fence brand receiver collars. Why pay the hefty prices of their batteries when you can buy a brand you can rely on for much less? Perimeter Technologies has designed a battery that will replace your current battery perfectly in R21, R22, R51, and Microlite models. With much effort placed in the making of your batteries, it is guaranteed you will get a great life expectancy out of your collar. Perimeter Technologies Batteries consist of a New and Improved Japanese cell lithium-ion and have a high energy density, also keeping the weight down from your dog's collar. With the components that make up this battery, it gives the power to last longer and has better safety factors than the normal battery. Bring confidence that your collar will last and go easy on your pocket by purchasing your battery.