Looking to buy my first HRM to use both on the bike and running. I see that Garmin is very popular. I don't really know what features I need. I understand with the Polars you can't change the battery yourself - but then how long does a battery last, this would be a PITA having to send it into Polar. I see the Garmin 60 on Ebay, can't find any info on this model. Is there anything else beside Garmin and Polar that is worth the $$$ ?