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I have a Polar watch with a Heart Rate Monitor T61 that I haven't used in years. I followed the manual to connect the watch to the monitor, but it failed. I suspect the battery is empty. I see no easy way to replace it.

How can I service the monitor and replace the battery?

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I found the answer in this thread, but because the pictures are missing and they would have been helpful, I'm posting a similar version with illustrations. (And I chose this StackExchange site since that thread is on a bike website and these watches serve to count bike speed.)

I used an X-acto knife to cut around the Polar logo at the front:

polar and knife

I cut to around 1cm depth. The knife seemed to reach the end of the thickness around the middle, so I used a screwdriver to lift it:

polar and screwdriver

screwdriver lifting middle part

And here is the result:

battery

I removed more material from the edges so the battery could come out, and slid the x-acto knife below the battery so I could force it out with the screwdriver:

battery about to come out

The battery is a CR2354 3V, wider at the base:

result

It is indeed empty. I'll order a new one, add padding to ensure electrical connection, then wrap it with electrical tape. If I need it underwater, I'll add silicone sealing.

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    Because sweat has salt and can be corrosive, consider using some sort of epoxy to seal that up after replacement. These days, this sort of non-serviceable design tends to be limited to units with rechargeable batteries.
    – Weiwen Ng
    Commented Mar 20 at 11:36
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    @WeiwenNg epoxy would make future replacement very difficult, as it's harder than the surrounding plastic. Better to use hot glue or (polyurethane) contact adhesive, after cleaning off the old glue. The latter is probably what was used in the first place, unless it's a latex-based glue.
    – Chris H
    Commented Mar 20 at 13:51
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    @ChrisH good point.
    – Weiwen Ng
    Commented Mar 20 at 15:43
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    Sand the front flat, 3d print a new front with an accomodation for battery changes, and epoxy that whole structure on. Bonus if it looks like something Tony Stark wears
    – Criggie ♦
    Commented Mar 21 at 9:56
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    This is an awful design. Normally you have a normal openable battery cover. If it is used often, it needs changing every few years. Perhaps this Polar one uses less energy and stays longer. I would not worry too much about the sweat if you cover it by an isolation tape.
    – Vladimir F Героям слава
    Commented Mar 21 at 16:27

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