heart rate monitor battery discharge excessive?

NeedToKNow · Yahoo User

I have replaced the battery two times in the last two months in my Polar F11 heart rate montior. The first battery lasted nearly 15 months. Why have the the last two batteries only lasted three weeks? I had them replaced at Batteries Plus.I use the HRM to caculate calories burned and heart rate percentage thus fitness . That is why I put the question here. I didn't know where else to put it.