I usually have to change batteries twice a year. There is a light on top of the mouse that is normally green. When the battery begins to run low, it will turn red but it doesn't stop right away. I haven't been caught with a dead mouse yet. I have a newer smaller wireless mouse for my laptop and the battery lifespan is 18 months. So far, so good. Also forgot to mention... I'm a lefty and I have a left-handed wireless mouse on my desktop. The shape matches my hand in the way that it is shaped... but since I'm used to a right-handed world, I switched the right and left click buttons to stay the same as the regular mouse since that is what I've always known.
Good to know about the wireless mouse. As you can tell I dont have one yet!!!! I'm thinking of getting one later this year.