Wireless Pet Containment Petsafe Wireless Instant Fence Pet Containment System?

Petsafe Wireless Instant Fence Pet Containment System? - wireless pet containment

I Petsafe wireless fence for over a month, and since the battery is weak. The lights are out, and he needed a new battery that I really wondered what the batteries just a few months? Away from the issuer at any time, it could also affect this too? And I have to buy the batteries online or otherwise can get?