How is the battery sealed into the chest strap, if you can tell? Is the case welded along a seam so that opening the battery case means breaking plastic? I remember that someone found a way to get that thing open and change the battery, although any warranty against moisture coming in was long gone.

It seems the fees on getting the battery changed by a factory representative can be expensive enough that some folks just buy a new HRM when the time comes.

I do not have a Polar, but have a Sigma BC-2006 I like a lot. All of its batteries are made to be changed by the user. "O" rings are used for the seals. Just twist a battery cover to the release position and let it fall out in your hand. Put in a new battery and twist the battery cover until it locks.