I love the Polar heart rate monitors for accuracy.  I had a cheap Polar HRM several yrs ago (like this one) and the battery lasted quite a while - a couple years.  It's too expensive to send in for battery replacement (costs as much as buying a new HRM), so I bought a deluxe Polar HRM model the next time - approx. $250.  The battery wore out really fast on the deluxe model and again, it was just too expensive to replace, so I just bought another cheap Polar HRM since I didn't want to make another investment in a "disposable" HRM.  I plan to research HRM's and switch to another brand of HRM that has batteries you can replace yourself.  The other con to this particular "cheap" model is that it picks up other people's heart rates in a spinning class where you are packed in.  Otherwise, it's great if you are out biking on your own or in a cardio class that is more spread out.  I love the Polar monitors, their durability, etc., but do not like the battery issue.  I'm looking at the Garmins for my next one.