I've been using a Polar S-710 heart rate monitor for cycling, biking, and running for two and a half years, with hardly a complaint. But finally, the watch receiver's battery has started to die. So, I decided to return the S-710 to Polar USA for battery service while I am travelling.
I'm having the battery replaced, rather than buying a new one, because I am happy with the feature set I have. There are a number of models that are slight enhancements to mine, such as the Polar S-720i which is aimed at cyclists, and the Polar S-610i which is more for runners. But, the S-710 has not been sufficiently superceded to make me part with over $200.
Polar USA recommends that the entire unit (receiver and transmitter strap) be returned to them for service. The instructions are on the Polar USA website. I understand that this can cost up to $59, but, they will replace the battery on one or both of the units, and (most importantly for me) clean and test them.
I'll report more on the service process when I get the HRM back from Polar.