Mine came with the battery dead. I had to unscrew about 9 miniature screws and get a cr2032 battery replacement. I don't know for sure how much time will the new battery give me, as the Speedo UV Meter is "always on" and taking UV measurements each 2 minutes, but I suspect I will be changing the battery quite often (and it is not a user friendly task). Also consider that the UV readout is given by a graphical bar, quite small, on the top of the lcd screen. It is NOT the actual UV index value. The manual gives you a conversion idea from bars quantity into UV index value ... but I cannot understand why the Speedo UV meter does not directly gives the numerical value , since the creen is big enough and has several numerical areas (date, time, alarm, etc.)