Save yourself some money and free yourself from that expensive Invisible Fence® Brand battery plan you are on from your local Invisible Fence® Brand dealer! We have batteries to fit your Invisible Fence® Brand collar as low as $8.67! (when purchasing the 12-pack) Shipping is just a dollar or two. We only charge actual shipping...NO up-charge on shipping. These batteries are guaranteed 100% compatible with your Invisible Fence® Brand R21 and R51 receiver. Our batteries batteries are an exact aftermarket replacement to the Invisible Fence® Brand Power Cap® battery. Satisfaction guaranteed! You’ll get quality batteries manufactured right here in the USA by Perimeter Technologies, Inc (not manufactured by Invisible Fence, Inc.). All of our Invisible Fence® Brand compatible batteries meet or exceed the original manufacturer’s specifications. Many dogs report getting a 6 month battery life out of each of our Invisible Fence® Brand compatible batteries. The shelf life on these batteries is at least six years.