Tired of paying inflated prices for your Invisible Fence Power Cap batteries?  You may want to try this.

I stumbled on this procedure awhile back.

FWIW, I have taken many factory Invisible Fence batteries apart and found they all had the same Duracell DL 1/3N battery inside. 

If you decide to try this I suggest using the same Duracell battery Invisible fence uses (DL 1/3N).

Click here for instructions (you will need Adobe Acrobat Reader)

The instructions state that using this procedure will void your warranty.  I cannot confirm nor deny this so proceed at your own risk.