The battery in my F11 only lasts about 3 months and then I need to change it. I bought it from someone, knowing that it had this problem so it is not an issue. CR2032 batteries are under $1.00 online and I buy them in bulk since I use them for other electronics I have. Sending it back to Polar was not an option since I was not the original owner and it is cheaper for me to just do it myself.