When I was using the HRM that came with my CS600 it worked flawlessly for me (have since stopped using it, but by no fault of the product.) I have one of the 'WearLink WIND' ones which have user replaceable batteries (the batteries were easy to find locally.) The different HRM/straps are on Polar's site, seems only the wearlink ones have replaceable batteries.
http://www.polar.fi/en/products/accessories