Actall's ATLAS One Button and Two Button Round Tags use a CR2032 battery; this can be provided by Actall or you can supply. To change the battery on the One Button and Two Button Round Tags, you must remove the cover to expose the compartment that houses the battery.
To remove the battery cover, hold the front face of the tag in one hand and press down and twist the back of the tag counter clock wise.
Remove the battery while taking care not to lose the rubber ring that creates a water resistant seal.
When placing the new battery into the compartment, be sure to insert the battery text-side up.
After replacing the battery, place the tag back in your hand, ensure you line the tag up with the gold colored programming strip to the left side of your hand and the back slightly to the left of the gold programming strip, push it down and twist clockwise to close the tag.