Battery Conspiracy

We have four different battery powered thermometers (each one is used for a different area of the body) and this week the batteries of all four of them went dead.  All of them had the original battery (the one that came with it when we purchased them).  Now this may not seem strange until you consider the different ages of each of these thermometers.  The first one we bought over 6 years ago.  The next one we bought right before Addison was born, so a little over 4 years ago.  The next one we bought after Hunter was born, so about 2 years ago.  And the last one we just bought a few months ago, before Ella was born.  So these thermometers have years of difference in when they were purchased, but yet, they all died THIS WEEK!