Which way round does the battery go in a Polar FS1 HRM watch?

this is f11 it may help you
http://timlaqua.com/2008/09/how-to-replace-the-battery-in-a-polar-f11-heart-rate-monitor-hrm/

I would think it is the sensor circuit in the watch. When you replaced the battery did you activate the processor all reset for the watch? I do not know on your model where or how this would be activated.

Electronic watches normally have a reset procedure for when the battery is changed. Very important the watch's processor reset is performed after changing the battery. This is not any of the user readings reset. This is a reset for the watch's processor and system. It is sometimes a contact that has to be shorted out with the jeweler's screwdriver, or it is a contact that has to be shunted, or etc., depending on the model. Maybe if you call the support for the watch they will tell you this. Normally they do not like the user opening the watch.

send your watch to an Authorized Polar Service Center, these are not designed to be user serviceable.

On my tips and tricks page is a link to the user manual.

The trick with the FS1 is that you have to wait between button pushes. Don't try to skip ahead of the pace of the watch, it is slow to set anything. That is the rub with 1 button operations.

Push the button, wait for the prompt, enter the info, push the button, wait for the prompt, etc.

if after trying this it still doesn't work you will either need to take it back and exchange or send into polar. There is a warranty service available. Again that link is under my tips and tricks.

Here is a video that shows the entire process of replacing the battery in the Polar fs1. It shows the little plate and where to place it.

If you go to http://www.polarusa.com/us-en/support/downloads?product=&category=User+manuals

You will see a drop down list. Scroll down to find the instructions for your model.

You have to remove band in order to fit caseback back onto the watch. Insert pocket knife blade between band and case lug and pry inwards. This motion should release the band. It will be a lot more difficult to fit the band back on and you will probably need to buy springbar tool. Rate me plz.

Like most makers, they recommend that you have batteries changed at one of there service centers (to retain the waterproof seal.

Some people have problems when refitting the backs of watches and come onto this site to find out how they can get their watch going again. The cost saving does not seem worth the risk of damaging your watch. If your watch is still under warranty, then it will be invalidated by unauthorised repairs.

To find your near service center, go to Ploar.com and click on "support" and then "service" and "retail finder.

"Gunk" is definately not good in any watch. If it got in there because your watch is not properly sealed then you would need to clean it out and get it properly sealed up again. Proper lubrication is necessary, but "gunk" should not be in there.

Someone posted a link on how to change the batter on an F11. If it's not longer under warranty or you just don't want to bother with sending it back and the extra costs, you could follow this: http://timlaqua.com/2008/09/how-to-replace-the-battery-in-a-polar-f11-heart-rate-monitor-hrm/