As a hear rate monitor this unit is really good and I like the software that comes with it (this is my third model of Polar monitors). But this is a replacement RS400 because the first one ran through batteries very quickly (to be fair I loved this watch when I first got it and I gave the first unit 5 stars in my review, albeit that was only after about a month of usage). The first battery lasted about four months, the second one four weeks. I don't suspect this is normal behavior though, it could just be a defect in the unit...or, as I have read on some of the Polar message boards, the watch is designed such that the side buttons are very easily pushed in when setting the watch down on its side such that it could be getting turned on inadvertently and running the battery down. My guess is that it is the latter rather than being a defect. Now I make sure not to put the watch down on its side to prevent this from happening. The watch is also designed so that, theoretically, you can change the battery yourself but the back is made of such soft plastic that it is almost impossible to open it without destroying the battery cover. This is very annoying. My last Polar was great because it had a metal back with small screws that were easy to pop out, change the battery, and pop back in. My guess is you have to have a special jewelers tool to get this back off without damaging the plastic. The conclusion I have come to is that I think this design is just a poor design. They need to go back to the screw on metal backs (e.g. 625Xi) and redesign the buttons to prevent the watch being accidentally turned on and draining the battery. I would recommend you look at a different Polar model as there are other designs that appear to be better and less likely to suffer from these issues.