The batteries in the Wi-Leash and PetFinders use small CR2032 button batteries which are cheap to replace and can last up to 90 days depending on model and usage. If you leave it on every day and it is being triggered every day, it may only last a few weeks or less. Both The Wi-Leash, PetFinder LR and PetFinder Multi all come with a silicone splash case(s) for the transmitter tag(s), so are resistant against rain and water splashes but are not submersible, e.g not to be used for swimming.