When it comes to PetSafe batteries, they are made to last you anywhere between 1 and 3 months.
The good thing, though, is you can buy replacement batteries ahead of time so you will always have replacements on hand.
One of the perks of PetSafes fencing systems is that they either come with replaceable batteries, or they come with rechargeable batteries.
How long the batteries last will depend on how often the collar is used as well.