Well my Invisible Fence Battery Subscription has run out, and I am going to need new batteries soon. While I can say that I am very happy with the Invisible Fence and the installation, however the batteries cost a fortune. For 1 year renewal battery plan, where Invisible fence ships you their batteries, the cost is $49 for 4 batteries. You do the math, you can go about 4 months before having to replace the batteries but they do last about 3 months. I found some instructions on taking the battery apart since the only thing unique about the battery is the housing. About the only thing you have to do is remove the black ring that is at the two prong (contact) end. You can use a small jewelers screwdriver or use a xacto knife. I used a stanley knife and stuck the tip of the blade in between the black ring and the grey housing. Be careful because the ring can fall off and is fragile. The battery is a Duracell 3V DL1/3N, which you can probably get at radio shack. Be sure to place the + end on the inside of the housing and the—(negative) end on the end where the two prongs are. I will post price and pics later.