I'm so glad I looked this up. VERY helpful. A simple Google search indicated that it took a 3 volt, flat 'coin' style battery. These batteries, however - I actually have in my desk at work in a 3 pack. No need to even take a trip to the store now. Oh, BTW - the 3 pack was purchased from Walgreens. They sell them in a 3 pack for around $10.