Giant writes – “Invisible Fence pet containment systems require a new battery in the dog’s collar every 3 months. Invisible Fence dealers sell battery packs for around $15. This expensive battery is a plastic case around a common CR1/3 battery, readily available from any hardware or drugstore for less than $5.00. Here is how to “renew” your battery in about 1 minute!”Link.

Update: Brian writes – Here’s something related you can post under “DIY Invisible Fence”:

You can pick up an inexpensive (under $200) Radio Fence kit at your local Agway, pet shop, etc. You have to install it yourself, but it’s not that difficult. Of course, you don’t get the training that you do with the Invisible Fence installation, but there’s a helpful video (looks like they come with a CD instead these days) if you want to do the training on your own.

We’ve had great luck with this. At our old house, the transmitter got damaged by lightning a couple of times, but the company replaced it very quickly, and it was cheap ($30 or something). Apparently, you can bury a big ol’ copper rod and ground it to that if you want, though.

The only downside is that you have to do all the maintenance. So, if a skunk decides to chew through the wire (yeah, this has happened :-), and you have a big area of coverage, it can take a while to figure out where the hole is. But you can use a long wire and a binary search approach to find that.

Also, the collars take a standard CR2302 battery.